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AGRICULTURAL 

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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  204 


GERM  CONTENT  OF  MILK 

II.  AS  INFLUENCED  BY  THE  UTENSILS 


BY  M.  J.  PEUCHA,  H.  M.  WEETER,  AND  W.  H.  CHAMBERS 


UEBANA,  ILLINOIS,  FEBRUARY,  1918 


CONTENTS  OF  BULLETIN  No.  204 

PAGE 

1.  INTRODUCTION 217 

2.  PREVIOUS  STUDIES  ON  UTENSILS '. 218 

3.  METHODS  OF  STUDY 219 

4.  PART  I. — INFLUENCE  SHOWN  BY  DIRECT  EXAMINATION  OF  UTENSILS 221 

Bacteria  Found  in  Freshly  Washed  Cans 221 

Bacteria  Found  in  Cans  Thirty  Hours  after  Being  Washed 226 

Bacteria  Found  in  Cans  Washed  and  Returned  to  the  Farm 229 

Sources  of  Bacteria  in  Washed  Cans 231 

Milk  as  the  Source  of  the  Bacteria 231 

Wash  Water  as  a  Source  of  the  Bacteria 233 

Bacteria  Found  in  Bottles  Freshly  Washed  and  in  Bottles  Standing 
Twenty-four  Hours 241 

5.  PART  II. — INFLUENCE  SHOWN  BY  EXAMINATION  OF  THE  MILK 245 

Collective  Influence  of  Utensils  at  the  Barn 245 

Influence  of  Unsteamed  Bottle  Filler  upon  Germ  Content  of  Milk ....  248 

Collective  Influence  of  Utensils  at  the  Barn  and  at  the  Dairy 250 

Influence  of  Individual  Utensils  at  the  Barn  and  at  the  Dairy 252 

6.  SUMMARY 255 

7.  CONCLUSIONS  .  ..257 


GERM  CONTENT  OF  MILK 
II.    AS  INFLUENCED  BY  THE  UTENSILS 

BY  M.  J.  PEUCHA,  ASSISTANT  CHIEF  IN  DAIRY  BACTERIOLOGY 
H.  M.  WEETER,  ASSISTANT  IN  DAIRY  HUSBANDRY,  and 
W.  H.  CHAMBERS,  ASSISTANT  IN  DAIRY  BACTERIOLOGY 

INTRODUCTION 

The  interval  during  which  milk  will  remain  sweet  is  an  important 
element  of  its  value,  and  one  for  which  the  producer  has  been  held 
mainly  responsible.  iMilk  sours  because  of  the  growth  in  it  of  plant 
life — bacteria. )  The  problem  of  protecting  the  keeping  quality  of  milk 
becomes  one  of  preventing  the  entrance  of  bacteria,  of  destroying  them 
after  they  enter,  or  of  keeping  them  so  cold  as  to  check  their  growth. 
The  first  interest  of  the  producer  is  to  restrict  the  number  of  bacteria 
getting  into  the  milk,  so  far  as  is  consistent  with  the  costs  involved. ; 
To  do  this  he  must  know  the  relative  importance  of  the  various  avenues 
thru  which  they  may  enter. 

Additions  to  our  knowledge  regarding  the  relative  importance  of 
the  various  avenues  thru  which  bacteria  enter  milk  have  been  fur- 
nished by  a  series  of  experiments  conducted  at  the  New  York 
(Geneva)3  and  the  Illinois2  Agricultural  Experiment  Stations.  The 
most  striking  result  of  these  studies  has  been  to  establish  the  fact  that 
ordinarily  barns  have  little  or  no  measurable  influence  upon  the  germ 
content  of  the  milk  produced  in  them. 

.  The  need  of  further  study  to  determine  the  mode  of  entrance  of 
the  large  number  of  bacteria  that  are  regularly  found  in  the  public 
milk  supply,  being  recognized,  this  investigation,  begun  in  the  fall  of 
1913,  was  directed  toward  determining  the  influence  that  the  various 
utensils  in  which  milk  is  normally  handled  exerts  upon  the  germ  con- 
tent of  the  milk. 


'Harding,  H.  A.,  Wilson,  J.  K.,  and  Smith,  G.  A.  Milking  Machines :  Effect 
of  Method  of  Handling  on  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr.  Exp. 
Sta,  Bui.  317.  1909. 

Harding,  H.  A.,  Wilson,  J.  K.,  and  Smith,  G.  A.  The  Modern  Milk  Pail. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  326.  1910.  • 

Harding,  H.  A.,  Ruehle,  G.  L.,  Wilson,  J.  K.,  and  Smith,  G.  A.  The  Effect  of 
Certain  Dairy  Operations  upon  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr. 
Exp.  Sta.  Bui.  365,  pp.  198-233.  1913. 

Harding,  H.  A.,  and  Wilson,  J.  K.  A  Study  of  the  Udder  Flora  of  Cows. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Tech.  Bui.  27.  1913. 

Ruehle,  G.  L.  A.,  and  Kulp,  W.  L.  Germ  Content  of  Stable  Air  and  Its  Effect 
upon  the  Germ  Content  of  Milk.  1ST.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  409,  pp.  418- 
474.  1915. 

^Prucha,  M.  J.,  and  Weeter,  H.  M.  Germ  Content  of  Milk:  I.  As  Influenced 
by  Factors  at  the  Barn.  111.  Agr.  Exp.  Sta.  Bui.  199.  1917. 

217 


218  BULLETIN  No.  204  [February, 

PREVIOUS  STUDIES  ON  UTENSILS 

In  1889,  H.  W.  Conn1  made  the  following  comment  on  the  influence 
of  utensils  upon  bacterial  contamination  of  milk  :x<  '  Vessels  in  which 
milk  and  cream  are  to  be  kept  are  a  great  source  of  contamination  of 
bacteria.  The  latter  gather  upon  the  sides  and  in  the  joints  and  de- 
velop in  the  minute  portions  of  milk,  grease,  and  other  matter  from 
which  it  is  difficult  to  free  the  vessels  completely  by  washing.  '  '^ 

Five  years  later  H.  L.  Russell,2  in  his  studies  on  milk  contamina- 
tion, examined  two  covered  pails.  One  pail  was  steamed  for  half  an 
hour  and  the  other  was  cleaned  in  the  ordinary  way  but  not  steamed. 
The  milk  received  into  the  sterilized  pail  had  a  germ  content  of  165 
bacteria  per  cubic  centimeter,  while  that  received  into  the  pail  not 
steamed  contained  4,265  bacteria  per  cubic  centimeter.  In  commenting 
later  on  the  contamination  of  milk  by  utensils,  this  author3  states  that 
'  '  dirty  vessels  are  a  prolific  source  of  trouble.  '  '  ^ 

In  1898,  Backhaus  and  Cronheim4  observed  that  passing  milk  over 
a  certain  cooler  raised  its  germ  content  from  11,500  to  33,000  bacteria 
per  cubic  centimeter.  In  1904,  Bergey5  concluded  from  his  studies 
on  milk  contamination  that  the  greater  portion  of  the  bacteria  with 
\vhich  milk  becomes  contaminated  is  derived  from  the  utensils.  In 
the  following  year,  Erf  and  Melick6  reported  that  cream  separators 
flushed  with  hot  water  at  night  after  being  used,  when  used  the  fol- 
lowing morning  added  to  the  germ  content  of  the  milk  passing  thru 
them,  some  millions  of  bacteria  per  cubic  centimeter  of  milk.  In  1906, 
Stewart7  reported  that  the  utensils  invariably  harbor  a  considerable 
number  of  bacteria.  He  found  that'  it  is  difficult  to  free  the  utensils 
from  germ  life  short  of  treatment  with  steam  under  pressure.  * 

Russell  and  Hoffmann8  found  that  when  milk  bottles  were  washed 
and  steamed  and  allowed  to  stand  twenty-four  hours,  the  bacteria 
multiplied  in  the  remnants  of  water  resulting  from  the  condensation 
of  the  steam.  , 


H.  W.     Bacteria  in  Milk  and  Its  Products.     Storrs  Agr.  Exp.   Sta. 
Bui.  4.     1889. 

2Russell,  H.  L.  Sources  of  Bacterial  Infection  and  the  Eolation  of  the  Same 
to  the  Keeping  Quality  of  Milk.  Wis.  Agr.  Exp.  Sta.  Ann.  Bpt.  11,  p.  152.  1894. 

'Eussell,  H.  L.  Tainted  and  Defective  Milks:  Their  Causes  and  Methods  of 
Prevention.  Was.  Agr.  Exp.  Sta.  Bui.  62.  1897. 

4B(ackhaus,  W.,  und  Cronheim,  W.  Tiber  aseptische  Milchgewinnung.  Ber. 
Landw.  Inst.  Univ.  Konigbs.,  1,  Heft.  2,  pp.  12-32.  1898. 

5Bergey,  D.  H.  Sources  and  Nature  of  Bacteria  in  Milk.  Penn.  Dept.  of 
Agr.  Bui.  125.  1904. 

•Erf,  O.,  and  Melick,  Chas.  "W.  Care  of  Dairy  Utensils.  Kans.  Agr.  Exp. 
Sta.  Bui.  131.  1905. 

TStewart.  A.  H.  Cleansing  of  Milk  Vessels:  Eelative  Value  of  Washing 
Powders.  Amer.  Med.,  2,  pp.  241-244.  1906. 

8Eussell,  H.  L.,  and  Hoffmann,  Conrad.  Bacteriological  Test  of  Bottle-Wash- 
ing Device.  Wis.  Agr.  Exp.  Sta.  Ann.  Ept.  22,  pp.  227-231.  1905. 


1913}  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  219 

The  various  studies  upon  the  milking  machines  by  Harrison,1  by 
Hastings  and  Hoffmann,2  Stocking  and  Mason,3  Meeker,4  and  Harding, 
Wilson,  and  Smith5  have  shown  that  the  germ  content  of  milk  may 
be  astonishingly  increased  thru  the  influence  of  the  milking  machine, 
tho  it  is  possible  to  keep  the  influence  of  the  machine  within  fair 
limits  provided  it  is  properly  handled. 

METHODS  OF  STUDY 

MT  "Washing  of  Utensils. — The  cans  used  in  this  study  were  from  two 
different  dairies.  In  both  dairies  the  method  of  washing  was  similar 
in  that  each  can  was  placed  in  a  vat  containing  one-percent  warm 
solution  of  sodium-carbonate  washing  powder,  and  scrubbed  with  a 
brush.  There  were,  however,  some  differences  in  the  conditions  and 
in  the  methods  employed  in  the  two  dairies.  In  Dairy  A  the  milk 
handled  in  the  cans  had  usually  a  low  germ  content ;  the  number  of 
cans  washed  in  the  same  lot  of  wash  water  was  from  20  to  30;  the 
amount  of  wash  water  used  was  60  gallons,  and  the  cans  were  rinsed 
after  being  washed.  In  Dairy  B  the  milk  handled  in  the  cans  invaria- 
bly had  a  high  germ  content ;  from  60  to  80  cans  were  washed  in  the 
same  lot  of  wash  water ;  the  amount  of  the  water  used  was  about  25 
gallons,  and  the  cans  were  not  rinsed  after  they  were  washed. 

All  other  utensils  studied  were  washed  in  Dairy  A.  In  the  case 
of  some  of  the  utensils,  such  as  the  bottle  filler,  the  above  method  of 
washing  could  not  be  employed ;  and  in  some  of  the  experiments  with 
cans,  the  method  of  washing  was  intentionally  altered.  Such  changes 
are  described  in  connection  with  the  respective  experiments. 

The  cans  in  Dairy  A  were  of  eight-gallon  capacity ;  those  in  Dairy 
B  were  of  five-,  eight-,  or  ten-gallon  capacity ;  and  the  bottles  were 
the  regular  quart  size. 

Determining  Number  of  Bacteria  in  Utensils. — Two  methods  were 
used  in  this  study  for  determining  the  number  of  bacteria  in  the  uten- 
sils. In  the  experiments  reported  in  Part  I  a  given  quantity  of  sterile 
water,  usually  one  liter,  was  poured  into  the  utensil  and  after  a  thoro 
shaking,  a  sample  of  this  water  was  taken  and  the  number  of  bacteria 


Garrison,  F.  C.  Machine  Drawn  Versus  Hand  Drawn  Milk.  Centbl.  Bakt. 
(etc.),  2  Abt.,  5,  183-189.  1899. 

"Hastings,  E.  G.,  and  Hoffmann,  Conrad.  Bacterial  Content  of  Machine 
Drawn  and  Hand  Drawn  Milk.  Wis.  Agr.  Exp.  Sta.  Ann.  Ept.  24,  pp.  214-223. 
1907. 

'Stocking,  W.  A.,  Jr.,  and  Mason,  C.  J.  Milking  Machines:  Part  I.  Effect 
upon  Quality  of  Milk.  Storrs  Agr.  Exp.  Sta.  Bui.  47.  1907. 

4Meeker,  E.  B.  Bacterial  Efficiency  of  the  Milking  Machine.  Penn.  Agr. 
Exp.  Sta.  Ann.  Ept.  for  the  year  1907-1908,  Part  II.  pp.  146-159.  1908. 

"Harding,  H.  A.,  Wilson  J.  K.,  and  Smith,  G.  A.  Milking  Machines:  Effect 
of  Method  of  Handling  on  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr.  Exp. 
Sta.  Bui.  317.  1909. 


220  BULLETIN   No.  204  [Felruary, 

in  it  determined.  This  obviously  falls  considerably  short  of  demon- 
strating the  full  amount  of  germ  life  present  in  the  utensils.  In  the 
experiments  reported  under  Part  II,  samples  were  taken  of  the  milk 
after  it  was  actually  poured  into  the  utensils  in  the  ordinary  opera- 
tions of  the  dairy,  and  the  difference  in  the  germ  content  of  the  milk 
handled  in  steamed  utensils  and  that  handled  in  unsteamed  utensils 
was  taken  as  the  measure  of  the  germ  content  of  the  unsteamed  uten- 
sils. This  method  evidently  more  closely  measures  the  true  influence 
of  the  utensils  upon  the  milk,  but  it  is  ordinarily  a  more  difficult  and 
expensive  form  of  experimentation. 

The  plate  method  was  used  for  counting  the  bacteria  in  these  sam- 
ples. Usually  two  or  three  dilutions  were  made  from  each  sample,  and 
three  plates  were  poured  from  each  dilution.  Every  count  recorded  in 
this  study  is  an  average  of  the  counts  from  at  least  three  plates.  The 
medium  used  in  making  these  counts  had  the  following  composition: 

Agar  shreds 15  grams 

Liebig  's  meat  extract 3  grams 

Witte  's  peptone 10  grams 

Lactose 10  grams 

Distilled  water    1  liter 

The  reaction  of  this  medium  was  adjusted  to  one  percent  normal  acid 
to  phenolphthalein.  The  plates  were  incubated  seven  days :  five  days 
at  20°  C.  and  two  days  at  37°  C. 

It  should  be  understood  that  this  method  of  counting  the  bacteria 
does  not  show  the  total  number  present.  It  was  used  because  among 
the  available  methods  of  making  such  determinations  this  one  seemed 
best  suited  to  the  problem. 


1918]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  221 

PART  I.— INFLUENCE  SHOWN  BY  DIRECT  EXAMINATION 

OF  UTENSILS 

Six  experiments  are  recorded  in  this  part  of  the  study,  five  of 
them  devoted  to  cans  and  one  to  bottles.  The  aim  in  these  experi- 
ments was,  first,  to  determine  the  number  of  bacteria  in  freshly  washed 
but  unsteamed  cans  and  bottles ;  second,  to  determine  whether  bacteria 
increase  in  utensils  that  are  washed  and  then  kept  for  a  period  of 
time  before  being  filled  with  milk ;  and  third,  to  determine  the  source 
of  these  bacteria. 

BACTERIA  FOUND  IN  FRESHLY  WASHED  CANS 

This  experiment  included  a  study  of  170  cans  that  had  been  used 
in  shipping  sweet  milk  from  the  farm  to  the  dairy.  The  cans  re- 
ported upon  in  Tables  1,  2,  and  3  came  to  Dairy  A  from  three  differ- 
ent farms,  and  those  in  Table  4  came  to  Dairy  B  from  thirty-four 
different  farms.  In  both  dairies  the  cans  were  washed  immediately 
after  the  milk  was  poured  from  them.  The  methods  of  washing  fol- 
lowed in  these  two  dairies  and  the  method  of  determining  the  germ 
life  remaining  in  the  cans  have  already  been  described  (page  219). 
The  length  of  time  intervening  between  the  washing  of  the  cans  and 
the  plating  of  the  water  with  which^they  were  rinsed  varied  from  one- 
half  to  four  hours. 

That  such  rinsing  did  not  remove  all  the  bacteria  from  the  uten- 
sils is  self  evident.  In  this  experiment,  therefore,  an  attempt  was  also 
made  to  determine  approximately  the  accuracy  of  the  method.  For 
this  purpose  each  can  in  Tables  1,  2,  and  3  was  rinsed  more  than 
once,  and  the  relation  between  the  number  of  bacteria  removed  by  the 
first  rinsing  and  that  removed  by  subsequent  rinsings  was  calculated. 
The  cans  in  Table  1  were  rinsed  twice  with  1,000  and  1,500  cc.  of 
sterile  water,  respectively;  those  in  Table  2  were  rinsed  four  times 
with  successive  one-liter  portions  of  sterile  water;  those  in  Table  3 
were  rinsed  four  times  with  successive  two-liter  portions  of  sterile 
.water ;  and  those  in  Table  4  were  rinsed  once  with  one  liter  of  sterile 
water. 

^Calculations  are  also  presented  which  show  what  the  increase  in 
the  germ  content  of  milk  would  have  been  had  the  total  number  of 
bacteria  removed  from  each  can  been  added  to  a  can  of  milks 

Arhe  results  of  this  experiment  are  significant  in  that  the  numbers 
of  bacteria  removed  from  the  washed  cans  by  rinsing  them  with  a 
small  quantity  of  sterile  water  were  large  and  variable./  More  than 
one  billion  bacteria  were  removed  from  each  of  39  of  the  114  cans 
washed  in  Dairy  A,  and  from  each  of  38  others  the  number  was  more 
than  one  hundred  million.  Even  larger  numbers  were  removed  from 
the  56  cans  washed  in  Dairy  B  ;  in  which  dairy,  it  will  be  recalled,  the 


222 


BULLETIN  No.   204 


[February, 


milk  as  it  was  received  had  a  higher  germ  content  than  that  received 
at  Dairy  A,  a  greater  number  of  cans  were  washed  in  a  smaller  amount 
of  water,  and  the  cans  were  not  rinsed  after  being  washed.  More  than 
one  billion  bacteria  were  removed  from  each  of  42  of  the  cans  in  this 
dairy,  and  in  only  4  cans  was  the  number  smaller  than  one  hundred 
million.  The  largest  number  removed  from  a  single  can  in  either 
dairy  was  96,666,000,000,  and  the  smallest  was  5,981,000. 

The  influence  of  such  large  numbers  of  bacteria  on  the  milk  may 
be  estimated  approximately  by  calculating  the  increase  in  the  germ 
content  of  a  can  of  milk  if  these  numbers  were  added  to  it.  The  two 
above  cans  with  the  maximum  and  minimum  numbers  were  of  ten-  and 
eight-gallon  capacity,  respectively.  If  the  minimum  number,  5,981,- 
000  bacteria,  were  added  to  eight  gallons  of  milk,  its  germ  content 

TABLE  1. — NUMBER  OF  BACTERIA  IN  FRESHLY  WASHED  CANS,  AS  DETERMINED  BY 
Two  SUCCESSIVE  EINSINGS:    DAIRY  A 


No. 

of 
can 

Number  of  bacteria  removed 
by  each  rinsing 

Total  number 
of  bacteria 
removed 

Increase  in 
germ  content 
of  can  of 
milk,  per  cc. 

Percentage 
of  bacteria 
removed  by 
1st  rinsing 

Binsed  with 
1,000  cc.  of 
sterile  water 

Einsed  with 
1,500  cc.  of 
sterile  water 

1 

16  400  000 

547  000 

16  947  000 

559 

97 

2 

16  560  000 

530  000 

17  090  000 

564 

97 

3 

38  840  000 

3  370  000 

42  210  000 

1394 

92 

4 

14  570  000 

680  000 

15  250  000 

503 

96 

5 

229  750  000 

11  320  000 

241  070  000 

7960 

95 

6 

312300000 

33  500  000 

345  800  000 

11425 

90 

7 

9  157  000  000 

810  000  000 

9  967  000  000 

329  100 

92 

8 

603  400  000 

122  000  000 

725  400  000 

23950 

83 

9 

61  000  000 

1  500  000 

62  500  000 

2064 

98 

10 

61  360  000 

1  550  000 

62  910  000 

2097 

98 

11 

13  000  000  000 

1877000000 

14  877  000  000 

491  300 

87 

12 

681  400  000 

308  600  000 

990  000  000 

32700 

69 

13 

16  040  000 

812  000 

16  852  000 

556 

95 

14 

50  470  000 

2  412  000 

52  882  000 

1746 

95 

15 

168  800  000 

30  000  000 

198  800  000 

6564 

85 

16 

83  560  000 

19  500  000 

103  060  000 

3404 

81 

17 

20  580  000  000 

3  150  000  000 

23  730  000  000 

783  600 

87 

18 

40  280  000 

12  075  000 

52  355  000 

1729 

77 

19 

2-0  940  000 

1  102  000 

22  042  000 

727 

95 

20 

52  000  000 

2  467  000 

54  467  000 

1799 

95 

21 

3  986  500  000 

317000000 

4  303  500  000 

142  150 

93 

22 

4  898  000  000 

485  000  000 

5  383  000  000 

177  750 

91 

23 

1  212  000  000 

57  700  000 

1  269  700  000 

41930 

95 

24 

4  302  000  000 

362  000  000 

4  664  000  000 

154  000 

92 

25 

2  413  000  000 

213  000  000 

2  626  000  000 

86720 

92 

26 

5  324  000  000 

370  000  000 

5  694  000  000 

188  000 

94 

27 

145  950  000 

30  775  000 

176  725  000 

5836 

83 

28 

104  500  000 

60  200  000 

164  700  000 

5439 

63 

29 

7  631  000  000 

1120000000 

8  751  000  000 

289  000 

87 

30 

80  640  000 

11  125  000 

91  765  000 

3030 

8-8 

31 

123  500  000 

58  750  000 

182  250  000 

6018 

68 

32 

33  290  000 

3  130  000 

36  420  000 

1202 

91 

1918} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


223 


TABLE  2. — NUMBER  OF  BACTERIA  IN  FRESHLY  WASHED  CANS,  AS  DETERMINED  BY 
FOUR  SUCCESSIVE  EINSINGS  WITH  ONE  LITER  OF  STERILE  WATER:    DAIRY  A 


No. 
of 
can 

Number  of  bacteria  removed  by  — 

Total  number 
of  bacteria 
removed 

Increase 
in  germ 
content 
of  can 
of  milk, 
per  cc. 

Percent- 
age of 
bacteria 
removed 
by  1st 
rinsing 

1st  rinsing 

2d  rinsing 

3d  rinsing 

4th  rinsing 

1 

339  633  000 

61767000 

33  133  000 

21  119  000 

455  652  000 

15  048 

75 

2 

10  466  000 

1271000 

589  000 

282  000 

12  608  000 

416 

83 

3 

796  499  000 

190  299  000 

143  299  000 

60  826  000 

1  190  923  000 

39324 

67 

4 

34  733  000 

6  433  000 

2  378  000 

160  000 

43  704  000 

1443 

79 

5 

11  366  O'OO 

959  000 

244  000 

161  000 

12  730  000 

420 

89 

6 

19  433  000 

893  000 

999  000 

173  000 

21  498  000 

709 

90 

7 

16  700  000 

1  360  000 

618  000 

411  000 

19  089  000 

630 

87 

8 

514  500  000 

243  300  000 

157  660  000 

61  000  000 

976  460  000 

32245 

53 

9 

20  850  000 

1  520  000 

259  000 

185  000 

22  814  000 

753 

91 

10 

427  850  '000 

60  000  000 

25  830  000 

19  466  000 

533  146  000 

17600 

80 

11 

2  863  333  000 

701  716  000 

436  000  000 

37  666  000 

4  038  715  000 

133  370 

71 

12 

95  000  000 

5  500  000 

1  700  000 

1  266  000 

103  496  000 

3418 

92 

13 

29  233  000 

6  096  000 

2  919  000 

1  932  000 

40  180  000 

1326 

73 

14 

6  549  333  000 

633  088  000 

489  166  000 

302  213  000 

7  973  800  000 

263  300 

82 

15 

64  400  000 

11  300  000 

6  338  000 

3  200  000 

85  238  000 

2814 

78 

16 

86  150  000 

22  400  000 

10  900  000 

6  516  000 

125  966  000 

4159 

68 

17 

2  800  000 

1  800  000 

989  000 

382  000 

5  981  000 

197 

47 

18 

18  800  000 

3  190  000 

2  541  000 

1  246  000 

25  777  000 

851 

73 

19 

2  370  000  000 

1  216  000  000 

706  100  000 

44  244  000 

4  336  344  000 

143  170 

55 

20 

668  000  000 

199  600  000 

95  150  000 

50  600  000 

1  013  350  000 

33450 

66 

21 

88  000  000 

15  150  000 

5  890  000 

1  244  000 

110  284  000 

3639 

80 

22 

175  000  COO 

26  900  000 

18  560  000 

14  195  000 

234  655  000 

7747 

.  75 

23 

368  000  000 

83  000  000 

49  200  000 

27  900  000 

528  100  000 

17430 

70 

24 

3  620  000  000 

890  000  000 

3.32  300  000 

20  200  000 

4  882  500  000 

161  200 

74 

25 

2  170  '000  000 

416  000  000 

304  600  000 

342  930  000 

3  233  530  000 

106  800 

67 

26 

1  610  000  000 

171  000  000 

82  000  000 

37  000  000 

1  900  000  000 

62  740 

85 

27 

97  450  000 

9  475  000 

10  870  000 

5  570  000 

123  365  000 

4075 

79 

28 

20  133  000  000 

2  843  000  000 

886  600  000 

895  000  000 

27  757  000  000 

916  600 

73 

29 

403  500  000 

59  850  000 

52  800  000 

27  900  000 

544  050  000 

17965 

74 

30 

3  590  000  000 

715  000  000 

174  700  QOO 

150  100  000 

4  629  800  000 

152  990 

78 

31 

525  500  000 

51  500  000 

28  400  000 

22  100  000 

627  500  000 

20740 

84 

32 

159  500  000 

14  100  000 

5  120  000 

3  040  000 

181  760  000 

6002 

88 

33 

222  000  000 

14  400  000 

6  825  000 

3  800  000 

247  025  000 

8156 

90 

34 

7  650  000  000 

2  720  000  000 

314  200  000 

410  700  000 

11  094  900  000 

366  400 

69 

35 

1  330  000  000 

134  350  000 

49  700  000 

39  800  000 

1  553  850  000 

51320 

86 

36 

1  557  000  000 

125  500  000 

91  900  000 

39  933  000 

1  814  333  000 

59900 

86 

37 

222  000  000 

15  000  000 

6  485  000 

3  700  000 

247  185  000 

8161 

90 

38 

32  930  000  000 

918  000  COO 

377300000 

36  888  000 

34  262  180  000 

1  131  000 

96 

39 

109  333  000 

98  667  000 

61  600  000 

57  533  000 

327  133  000 

10  800 

33 

40 

561  333  000 

171  667  000 

73  400  000 

554  000 

806  954  000 

26710 

69 

41 

78  133  000 

23  983  000 

11  750  000 

6  010  000 

119876000 

3958 

65 

42 

2  150  667  000 

431  333  000 

201  000  000 

125  000  000 

2  908  000  000 

96040 

74 

43 

154  000  000 

78  867  000 

43  467  000 

28  866  000 

305  200  000 

10080 

51 

44 

216  000  000 

70  667  000 

19  633  000 

21007000 

327  367  000 

10810 

66 

45 

528  666  000 

47  044  000 

28367000 

29  833  000 

633  910  000 

20930 

83 

46 

350  000  000 

77  933  000 

35  000  000 

30  733  000 

493  666  000 

16300 

71 

47 

1  036  667  000 

286  667  000 

119600000 

84  133  000 

1  427  007  000 

47120 

73 

48 

1  710  000  000 

612007000 

219033000 

180  750  000 

2  722  450  000 

89800 

63 

49 

1  935  333  000 

461  333  000 

209  533  000 

158  667  000 

2  764  866  000 

91300 

70 

50 

2  720  '000  000 

756  000  000 

213  200  000 

272  000  000 

3  961  200  000 

130  800 

69 

224 


BULLETIN  No.  204 


[February, 


would  be  increased  by  197  bacteria  per  cubic  centimeter.  If  96,666,- 
000,000  bacteria,  the  maximum  number  found  in  a  single  can,  were 
added  to  ten  gallons  of  milk,  its  germ  content  would  be  increased  by 
2,557,000  bacteria  per  cubic  centimeter.  If  all  the  bacteria  removed 
from  the  32  eight-gallon  cans  listed  in  Table  1  were  added  to  256 
gallons  of  milk  (the  total  capacity  of  the  cans),  its  germ  content  would 
be  increased  by  87,657  bacteria  per  cubic  centimeter.  Corresponding 
calculations  for  Tables  2,  3,  and  4  would  show  an  average  increase  in 
the  germ  content  of  the  milk,  of  87,059,  47,863,  and  291,790  bacteria, 
respectively. 

Of  the  170  cans  recorded  in  these  tables,  54,  or  31.8  percent,  would 
have  added  more  than  100,000  bacteria  per  cubic  centimeter  of  milk ; 

TABLE  3. — NUMBER  OP  BACTERIA  IN  FRESHLY  WASHED  CANS,  AS  DETERMINED  BY 
FOUR  SUCCESSIVE  EINSINGS  WITH  Two  LITERS  OF  STERILE  WATER  :   DAIRY  A 


No. 

of 
can 

Number  of  bacteria  removed  by  — 

Total  number 
of  bacteria 
removed 

Increase 
in  germ 
content 
of  can 
of  milk, 
per  ce. 

Percent- 
age of 
bacteria 
removed 
by  1st 
rinsing 

1st  rinsing 

2d  rinsing 

3d  rinsing 

4th  rinsing 

1 

35  334  000 

2  466  000 

f   1  466  000 

1066000 

40  332  000 

1331 

87 

2 

122  666  000 

18  866  000 

17  000  000 

12  068  000 

170  600  000 

5634 

72 

3 

374  666  000 

192  666  000 

109  334  000 

104  666  000 

781  332  000 

25800 

48 

4 

300  000  000 

87000000 

33  466  000 

33  614  000 

454  200  000 

14990 

66 

5 

•  28  666  000 

4  666  000 

2  666  000 

1  066  000 

37  064  000 

1224 

77 

6 

5  146  666  000 

1  888  000  000 

1  237  334  000 

858  666  000 

9  130  666  000 

301  500 

56 

7 

40  666  000 

1  134  000 

600  000 

334  000 

42  534  000 

1404 

95 

8 

111  000  000 

13  666  000 

7868000 

4  634  000 

137  168  000 

4530 

81 

9 

25  334  000 

2  400  000 

934  000 

932  000 

39  600  000 

1307 

85 

10 

37  666  000 

5  000  000 

2000000 

1  800  000 

45  466  000 

1502 

80 

11 

1  746  666  000 

320  000  000 

233  334  000 

148  666  000 

2  448  666  000 

80840 

71 

12 

1  016  666  000 

238  666  000 

263  334  000 

138  968  000 

1  657  634  000 

54720 

61 

13 

594  666  00-0 

282  000  000 

179  600  000 

151066000 

1  207  332  000 

39880 

49 

14 

80  666  000 

8  200  000 

2  866  000 

2  068  000 

93  800  000 

3098 

86 

15 

54  666  000 

1  200  000 

1  532  000 

466  000 

57  864  000 

1910 

94 

16 

5  310  000  000 

997  000  000 

536  000  000 

414  666  000 

7  357  666  000 

242  960 

73 

17 

46  000  000 

2  934  000 

600  000 

532  000 

50  066  000 

1652 

92 

18 

234  000  000 

4  414  000 

3  800  000 

934  000 

293  268  000 

9685 

96 

19 

4  320  000  000 

714  000  000 

582  000  000 

351334000 

5977334000 

197  080 

72 

20 

13  334  000 

1  800  000 

1  266  000 

400  000 

16  800  000 

554 

79 

21 

42  666  000 

2  344  000 

724000 

466  000 

46  200  000 

1524 

92 

22 

78  000  000 

7  866  000 

3  266  000 

2  334  000 

91  466  000 

3020 

85 

23 

3  186  666  000 

574  000  000 

466  000  000 

354  000  000 

4  780  666  000 

157  840 

71 

24 

78  666  000 

6  800  000 

4  400  000 

2  734  000 

92  600  000 

3058 

85 

25 

2500000000 

462  666  000 

327  000  000 

194  000  000 

3  483  666  000 

115  020 

72 

26 

766  666  000 

186  000  000 

204  134  000 

45  600  000 

1  203  000  000 

39740 

64 

27 

55  000  000 

4  534  000 

2  134  000 

2  400  000 

64  068  000 

2116 

86 

28 

322  666  000 

41  334  000 

18  000  000 

20  066  000 

402066000 

13274 

80 

29 

637  000  000 

128*14000 

64  034  000 

58  168  000 

888  136  000 

29320 

72 

30 

170  666  000 

8  400  000 

10  600  000 

3  600  000 

193  266  000 

6384 

88 

31 

78  666  000 

7  066  000 

1  800  000 

1  800  000 

89  332  000 

2950 

88 

32 

3  226  666  000 

928  666  000 

575  334  000 

293  334  000 

5  004  000  000 

365220 

64 

GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


225 


54  would  have  added  more  than  10,000  and  less  than  100,000  bacteria; 
and  62  cans,  or  36.4  percent,  would  have  added  less  than  10,000. 

The  data  in  Tables  1,  2,  and  3  demonstrate  that  when  milk  cans 
are  rinsed  more  than  once,  the  first  rinsing  always  removes  a  larger 
number  of  bacteria  than  any  subsequent  single  rinsing.  When  four 
rinsings  were  made  in  succession,  in  78  out  of  82  cases  the  first  rinsing 
alone  removed  more  bacteria  than  all  three  subsequent  rinsings.  The 
data  also  indicate,  with  only  fifteen  exceptions,  that  any  one  of  the 
consecutive  rinsings  of  a  can  removes  more  bacteria  than  any  subse- 
quent rinsing. 

If  the  total  number  of  bacteria  removed  from  each  can  by  all  the 
rinsings  is  taken  as  100  percent,  the  calculations  will  show  that  from 
110  of  the  114  cans  the  first  rinsing  removed  more  than  50  percent 
of  the  bacteria.  The  highest  percentage  removed  by  the  first  rinsing 
was  97,  and  the  lowest  was  33.  The  average  percentage  removed  by 
the  first  rinsing  of  the  cans  rinsed  only  twice,  once  with  1,000  cc.  and 
once  with  1,500  cc.  of  water  (Table  1),  was  89;  for  the  cans  rinsed 


TABLE  4. — NUMBER  OF  BACTERIA  IN  FRESHLY  WASHED  CANS,  AS  DETERMINED  BY 
ONE  EINSING  WITH  ONE  LITER  OF  STERILE  WATER:    DAIRY  B 


No. 
of 
can 

Capac- 
ity, 

gal. 

Number  of 
bacteria  re- 
moved by 
rinsing 

Increase  in 
?erm  content 
of  can  of 
milk,  per  cc. 

No. 
of 
can 

Capac- 
ity, 
gal. 

Number  of 
bacteria  re- 
moved by 
rinsing 

Increase  in 
germ  content 
of  can  of 
milk,  per  cc. 

1 

5 

7  360  000  000 

389  400 

29 

10 

7  133  000  000 

188  700 

2 

8 

I  960  000  000 

64730 

30 

5 

30  000  000  000 

1587300 

3 

8 

490  000  '000 

16180 

31 

10 

17  466  000  000 

462  080 

4 

10 

3  680  000  000 

97350 

32 

5 

1  853  000  000 

98040 

5 

5 

1  430  '000  000 

75660 

33 

10 

96  666  000  000 

2  557  000 

6 

8 

1  390  000  000 

45900 

34 

8 

886  000  000 

29260 

7 

8 

1  590  000  000 

52500 

35 

5 

4  366  000  000 

231  000 

8 

5 

5  690  000  000 

301  050 

36 

5 

806  000  000 

42640 

9 

5 

222  000  000 

11740 

37 

8 

60  000  000 

1981 

10 

8 

2  310  000  000 

76290 

38 

5 

90  000  000 

4760 

11 

.   8 

2  940  000  000 

97100 

39 

8 

2  240  000  000 

73970 

12 

8 

11070000000 

353360 

40 

5 

2  486  000  000 

131  540 

13 

10 

8  550  000  000 

226  180 

41 

8 

8  883  000  000 

293  360 

14 

8 

38  670  000  000 

1  277  000 

42 

8 

190  000  000 

62740 

15 

8 

8  730  000  000 

288  300 

43 

5 

1  500  000  000 

79360 

16 

5 

1  596  000  000 

84450 

44 

5 

2  690  000  000 

142  330 

17 

10 

330  000  000 

8730 

45 

8 

143'000  000 

4722 

18 

8 

7  446  000  000 

245  900 

46 

8 

2  533  000  000 

83650 

19 

5 

•  8  860  000  000 

468  800 

47 

10 

14  000  000  000 

370  300 

20 

8 

8  566  000  000 

282  880 

48 

8 

6  200  000  000 

204  740 

21 

5 

736  000  000 

38940 

49 

5 

4  186  000  000 

221  480 

22 

5 

250  000  000 

13230 

50 

8 

18  830  000  000 

621  800 

23 

5 

256000000 

13540 

51 

10 

9  133  000  000 

241  600 

24 

5 

2  560  000  000 

135  450 

52 

8 

19  666  000  000 

649  400 

25 

5 

16  360  000  000 

865  600 

53 

10 

11  233  000  000 

297  150 

26 

5 

83  000  000 

4390 

54 

8 

66  000  000 

2179 

27 

5 

2  106  000  000 

109  000 

55 

8 

3  100  000  000 

102  370 

28 

5 

23  660  000  000 

1  251  800 

56 

8 

3  160  000  000 

104  350 

226  BULLETIN  No.  204  [February, 

four  times  with  one  liter  of  water  (Table  2),  it  was  74.6 ;  and  for  the 
cans  rinsed  four  times  with  two  liters  of  water  (Table  3),  it  was  77. 
The  results  of  these  observations  on  170  cans  suggest  that  milk 
cans  when  washed  in  the  ordinary  manner  contain  sufficient  germ  life 
to  heavily  inoculate  the  milk  later  placed  in  them.  The  results  of 
successive  rinsings  with  sterile  water  suggest  that  while  the  germ  life 
removed  by  the  first  rinsing  amounts  to  a  considerable  fraction  of  the 
germ  life  in  the  can,  it  is  by  no  means  the  entire  germ  life  present. 
Accordingly,  the  germ  content  as  determined  in  this  manner  is  dis- 
tinctly below  the  true  number  of  bacteria  actually  present  in  the  uten- 
sil under  investigation. 

BACTERIA  FOUND  IN  CANS  THIRTY  HOURS  AFTER  BEING  WASHED 

In  the  preceding  experiment  it  was  shown  that  freshly  washed 
cans  invariably  harbored  large  numbers  of  bacteria.  In  dairy  practice 
the  utensils,  however,  are  not  commonly  used  for  milk  immediately 
after  they  are  washed.  This  is  especially  true  of  cans  in  which  milk 
is  shipped  from  the  farm  to  the  dairy.  Such  cans  are  washed  and 
usually  steamed  at  the  dairy ;  then  covered  with  the  lids  and  returned 
to  the  farm,  where  they  are  frequently  used  for  milk  without  any 
further  treatment.  At  times,  one  or  even  two  days  will  elapse  be- 
tween the  washing  of  the  cans  and  their  use. 

f  This  experiment  was  designed,  therefore,  to  determine  the  germ 
life  in  cans  at  the  time  they  would  ordinarily  be  used.  %Thc  160  eight- 
gallon  cans  examined  were  washed  in  Dairy  A.  One  hundred  of  these 
were  steamed,  while  sixty  were  left  unsteamed. 

The  steaming  consisted  of  holding  each  can  over  a  jet  of  steam 
at  15  pounds  pressure  for  25  seconds.  The  pressure  of  the  steam  was 
measured  by  a  gage  placed  between  the  valve  and  the'  jet  opening. 
Other  experiments  upon  steaming  cans  in  this  manner  showed  that  if 
cans  so  treated  were  filled  with  milk  immediately  afterward,,  they 
rarely  added  more  than  2  bacteria  per  cubic  centimeter  to  the  milk. 
Fifty  of  the  steamed  cans  and  fifty  of  those  not  steamed  were  inverted 
en  a  rack  with  the  lids  off.  The  other  fifty  steamed  cans  and  the  ten 
not  steamed  were  closed  immediately  after  washing.  All  the  cans 
were  then  kept  th'irty  hours  in  a  room  having  a  humidity  of  40  per- 
cent and  a  temperature  of  60°  to  70°F.  The  number  of  bacteria  found 
in  each  can  is  shown  in  Table  5. 

The  fifty  cans  that  were  washed,  steamed,  and  then  held  thirty 
hours  uncovered  and  inverted  on  a  rack  were  dry  and  free  from  bad 
odor.  The  number  of  bacteria  found  in  them  was  small  in  all  cases. 
Only  3  of  the  fifty  cans  had  more  than  one  million  bacteria  and  36 
of  them  had  less  than  100,000.  If  the  bacteria  found  in  these  fifty 
cans  were  added  to  400  gallons  of  milk,  the  germ  content  of  this 


1918} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


227 


TABLE  5. — NUMBER  OF  BACTERIA  IN  STEAMED  AND  IN  UNSTEAMED  CANS  HELD 

THIRTY  HOURS  AFTER  TREATMENT:    DAIRY  A 
(As  determined  by  rinsing  with  one  liter  of  sterile  water) 


Steamed  cans  held  30  hours 

Unsteamed  cans  held  30  hours 

Uncovered  and 
inverted  on  a 
rack 

Covered  with 
their  lids 

Uncovered  and 
inverted  on  a 
rack 

Covered  with 
their  lids 

No. 
of 
can 

No.  of 
bacteria 

No. 

of 
can 

No.  of 

bacteria 

No. 
of 
can 

No.  of 

bacteria 

No. 
of 
can 

No.  of 
bacteria 

1 

20000 

51 

10000 

101 

164  000  000 

151 

6  910  000  000 

2 

20000 

52 

60000 

102 

148  000  000 

152 

5  520  000  000 

3 

20000 

53 

66  000  000 

103 

6  000  000 

153 

4  150  000  000 

4 

30000 

54 

6  800  000 

104 

170-000  000 

154 

4  300  000  000 

5 

30000 

55 

3  260  000 

105 

190  '000  000 

155 

6  000  000  000 

6 

20000 

56 

15  000  000 

106 

17  000  000  000 

156 

2  1-00  000  000 

7 

40000 

57 

10  600  000 

107 

7  300  000  000 

157 

1  400  000  000 

8 

10  '000 

58 

11  600  000 

108 

44  000  000 

158 

6  250  000  000 

9 

20000 

59 

21300000 

109 

3  000  000 

159 

1  900  '000  000 

10 

240  000 

60 

220  000 

110 

22  000  '000 

160 

450  000  000 

11 

100  000 

61 

60  000  000 

111 

10  100  000  000 

12 

290  000 

62 

210  000 

112 

1  000  O'OO 

13 

700  000 

63 

110  000 

113 

135  000  000 

14 

40000 

64 

30000 

114 

1  000  000 

15 

60000 

65 

2  13  000  '000 

115 

303  '000  000 

16 

600-00 

66 

39  000  000 

116 

76000000 

17 

600  000 

67 

550  000 

117 

8  000  000 

18 

1  450  000 

68 

48  000  000 

118 

9  000  O'OO 

19 

50000 

69 

14  100  000 

119 

94  000  000 

20 

430  '000 

70 

2  180  000 

120 

59  000  000 

21 

90000 

71 

2  260  000 

121 

14  000  000 

22 

30000 

72 

4  800  000 

122 

3  000  O'OO 

23 

30000 

73 

210  000 

123 

42  000  000 

24 

5000-0 

74 

110  000  000 

124 

22  000  000 

25 

330  000 

75 

14  500  000 

125 

278  000  000 

26 

150  000 

76 

210  '000 

126 

4  700  000  000 

27 

90000 

77 

35  500  000 

127 

48  000  000 

28 

30000 

78 

7  000  000 

128 

2  000  000 

29 

80000 

79 

1  310  000 

129 

10  000  000 

30 

30000 

80 

35  '000  000 

130 

21  000  000 

31 

30000 

81 

130  000 

131 

8  000  000 

32 

60000 

82 

4  380  000 

132 

1  000  000 

33 

50000 

83 

78  000  000 

133 

1  000  000 

34 

90000 

84 

240  000 

134 

17  000  O'OO 

35 

60000 

85 

12  500  000 

135 

1  000  000 

36 

20  000 

86 

89  000  000 

136 

48  000  000 

37 

2  720  000 

87 

43  000  000 

137 

1  000  000 

38 

30000 

88 

1  190  000  000 

138 

3  000  000 

39 

120  000 

89 

33  000  000 

139 

1  000  000 

40 

30  000 

90 

67  000  000 

140 

3  000  '000 

41 

3  700  000 

91 

240  000 

141 

2  000  000 

42 

100  000 

92 

50  000  000 

142 

2  000  000 

43 

50000 

93 

270  000  000 

143 

43  000  000 

44 

20  000 

94 

240  000 

144 

2  000  000 

228 


BULLETIN  No.  204 


[February, 


TABLE  5. — Concluded 


Steamed  cans  held  30  hours 

Unsteamed  cans  held  30  hours 

Uncovered  and 
inverted  on  a 
rack 

Covered  with 
their  lids 

Uncovered  and 
inverted  on  a 
rack 

Covered  with 
their  lids 

No. 
of 
can 

No.  of 
bacteria 

No. 

of 
can 

No.  of 

bacteria 

No. 
of 
can 

No.  of 
bacteria 

No. 
of 
can 

No.  of 

bacteria 

45 

30000 

95 

149  000  000 

145 

5  000  000 

46 

40000 

96 

710  000 

146 

2  000  000 

47 

330  000 

97 

590  000 

147 

2  000  000 

.      48 

80000 

98 

16  000  000 

148 

3  000  000 

49 

60  000 

99 

550  000 

149 

5  000  000 

50 

30000 

100 

22  000  000 

150 

170  000 

Average  no. 
of  bacteria 

per  can 

255,800 

54  988  000 

822  463  400 

3  898  000  000 

Average  no. 
of  bacteria 

per  cc.  in 
can  of  milk 

8 

1816 

27164 

128  730 

amount  of  milk  would  be  increased  by  8  bacteria  per  cubic  centi- 
meter. Whether  any  bacterial  growth  took  place  in  these  cans  during 
the  thirty  hours  is  not  certain,  but  the  results  show  that  cans  so  treated 
have  a  negligible  effect  upon  the  germ  content  of  milk. 

The  fifty  cans  that  were  washed,  steamed,  and  then  held  thirty 
hours  with  the  lids  on,  were  still  wet  and  most  of  them  had  a  more 
or  less  pronounced  odor.  These  cans  had  a  much  larger  number  of 
bacteria  than  those  steamed,  uncovered,  and  inverted.  Only  3  of  the 
fifty  cans  had  less  than  100,000  bacteria,  and  in  34  the  number  was 
over  one  million.  If  the  bacteria  found  in  these  fifty  eight-gallon  cans 
were  added  to  400  gallons  of  milk,  its  germ  content  would  be  increased 
by  1,816  bacteria  per  cubic  centimeter. 

The  fifty  cans  that  were  washed  but  not  steamed  and  were  then 
held  thirty  hours  uncovered  and  inverted,  were  dry.  None  of  the  cans 
had  a  bad  odor,  altho  most  of  them  were  not  what  is  called  "sweet 
smelling."  The  number  of  bacteria  in  them  was  much  larger  than  in 
the  cans  steamed  and  inverted.  Only  one  of  the  fifty  cans  had  less  than 
one  million  bacteria,  in  24  of  them  the  numbers  of  bacteria  were  be- 
tween one  million  and  ten  'millions,  and  4  cans  had  over  a  billion 
bacteria  each.  If  the  bacteria  found  in  all  these  cans  were  added  to 
400  gallons  of  milk,  its  germ  content  would  be  increased  by  27,164 
bacteria  per  cubic  centimeter.  It  is,  however,  to  be  observed  that  this 
average  number  does  not  give  an  accurate  idea  of  the  condition  of 
these  cans  since  the  total  number  of  bacteria  found  in  the  fifty  cans 
was  41,123,170,000,  and  of  this  number  39,100,000,000  were  contri- 
buted by  only  4  cans  and  2,023,170,000  by  the  remaining  46  cans.  The 


191S]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  229 

germ  content  of  milk  in  these  46  cans  would  have  averaged  only  1,336 
bacteria  per  cubic  centimeter.  The  destructive  effect  of  the  drying  of 
the  cans  upon  the  germ  life  in  them  is  evident  from  a  comparison  of 
these  results  with  those  obtained  from  the  freshly  washed  cans  reported 
in  Tables  1,  2,  and  3. 

The  ten  cans  that  were  washed  but  not  steamed  and  then  were 
covered  and  held  thirty  hours  had  in  all  cases  a  decidedly  bad  odor 
and  they  also  contained  large  numbers  of  bacteria.  Nine  of  the  ten 
cans  showed  over  a  billion  bacteria  each.  If  the  total  number  of 
bacteria  found  in  these  ten  eight-gallon  cans  were  added  to  80  gallons 
of  milk,  its  germ  content  would  have  been  increased  by  128,730  bacteria 
per  cubic  centimeter. 

f  It  is  evident  from  these  results  that  pronounced  bacterial  growth 
took  place  in  the  cans  that  were  covered  and  allowed  to  stand  for 
thirty  hours.  Bacterial  growth  in  general  is  conditioned  by  three 
factors :  temperature,  food,  and  moisture,  jf  All  -the  cans  in  this  ex- 
periment were  held  at  the  same  temperature  and  were  washed  in  the 
same  dairy  by  the  same  operator,  so  that  the  principal  difference  be- 
tween the  covered  and  the  uncovered  cans  was  the  persistance  of 
moisture  in  the  covered  cans.  These  results  point  to  the  conclusion 
that  it  is  very  difficult  to  wash  cans  so  that  no  bacterial  food  is  left 
in  them,  and  if  the  cans  are  then  covered  without  being  dried,  and 
are  allowed  to  stand  for  a  period  of  time,  the  bacteria  in  them  increase 
to  large  numbers. 

• 

BACTERIA  FOUND  IN  CANS  WASHED  AND  RETURNED  TO  THE  FARM 

This  experiment  was  designed  to  measure  the  germ  life  in  cans 
that  were  washed  and  returned  to  several  dairy  farms  ready  for  use/ 
In  order  to  maintain  the  usual  conditions  in  this  dairy  (Dairy  A),  no 
interference  was  made  in  any  of  the  usual  operations  and  the  men 
doing  the-  work  were  not  aware  of  the  experiment.  No  record  could 
be  obtained  of  the  exact  treatment  of  the  individual  cans,  but  in  gen- 
eral each  can  was  washed,  rinsed,  steamed  over  a  jet,  and  covered  with 
a  lid.  Casual  observations  indicated  that  the  steaming  of  the  cans 
varied  from  five  to  twenty  seconds  per  can. 

The  treatment  of  the  cans  at  the  farms  was  not  uniform.  At  times 
they  were  inverted  on  a  rack,  with  lids  off,  and  at  other  times  they 
were  not  opened  until  used.  The  time  intervening  between  the  wash- 
ing of  the  cans  and  their  use  varied  from  six  to  forty  hours. 

Just  before  the  cans  were  used  for  milk  they  were  rinsed  with 
one  liter  of  sterile  water  and  the  germ  content  of  this  water  was  de- 
termined. Table  6  presents  the  results  of  the  examination  of  91  cans. 

As  in  the  other  experiments,  the  numbers  of  bacteria  found  in  these 
cans  were  varied  and  in  some  cases  large.  Can  43,  for  example,  showed 
80.000  bacteria,  and  Can  66  showed  30,830,000,000  bacteria.  Of  the 


230 


BULLETIN  No.  204 


[February, 


TABLE  6. — NUMBER  OF  BACTERIA  IN  CANS  AFTER  THEY  WERE  WASHED  AND  STEAMED 

IN  THE  DAIRY  AND  EETURNED  TO  THE  FARM:    DAIRY  A 
(As  determined  by  rinsing  with  one  liter  of  sterile  water) 


No. 
of 
can 

Number  of 
bacteria 
in  cans 

Increase  in  germ 
content  of  can 
of  milk,  per  ce. 

No. 
of 
can 

Number  of 
bacteria 
in  cans 

Increase  in  germ 
content  of  can 
of  milk,  per  cc. 

1 

56  950  000 

1880 

47 

133  833  000 

4420 

2 

636  500  000 

21020 

48 

47  750  000 

1577 

3 

388  000  000 

12870 

49 

149  000  000 

4920 

4 

1  400  000 

46 

50 

675  000  000 

22290 

5 

1  400  000 

46 

51 

10  950  000  000 

361  600 

6 

1  505  000  000 

49  700 

52 

995  000  000 

32860 

7 

107  500  000 

3555 

53 

83  100  000 

2744 

8 

4  550  000 

150 

54 

•   520  000  000 

17170 

9 

74750000 

2468 

55 

16  720  000 

552 

10 

42  700  000 

1387 

56 

168  700  000 

5570 

11 

26400000 

871 

57 

19  570  000 

646 

12 

21300000 

703 

58 

26  500  000 

875 

13 

11  375  000 

375 

59 

90  640  000 

2993 

14 

80  650  000 

2633 

60 

988  000 

30 

15 

37  000  000 

1222 

61 

39  900  000 

1317 

16 

162  025  000 

5320 

62 

1  187  000  000 

39190 

17 

37  225  000 

1229 

63 

1  900  000 

62 

18 

55  075  000 

1819 

64 

1  949  000  000 

64340 

19 

82  000  000 

2708 

65 

581  000  000 

19200 

20 

24  975  000 

825 

66 

30  83-0  000  000 

1  018  000 

21 

37  325  000 

1233 

67 

30  280  000 

1000 

22 

488  000  000 

16110 

68 

82  900  000 

2737 

23 

400  000  000 

13210 

69 

41  025  000 

1355 

24 

20  500  000 

677 

70 

68  850  000 

2273 

25 

36  000  000 

1187 

71 

51  960  000 

1716 

26 

102  000  000 

3368 

72 

62  900  000 

2077 

27 

22  -000  000 

726 

73 

125  350  000 

4140 

28 

17  000  000 

561 

74 

56  210  000 

1856 

29- 

2  045  000  000 

67530 

75 

80  030  000 

2642 

30 

382  000  000 

12610 

76 

.  40  000  000 

1340 

31 

63  500  000 

2097 

77 

112  700  000 

3722 

32 

36  000  000 

1189 

78 

59  050  OO'O 

1950 

33 

83  000  000 

2742 

79 

506  700  000 

16730 

34 

5  500  000 

187 

80 

79  070  000 

2611 

35 

4  500  000 

148 

81 

28  820  000 

951 

36 

354  500  000 

11  700 

82 

1  698  000  000 

56070 

37 

42  000  000 

1387 

83 

42  730  000 

1411 

38 

3  270  000  000 

108  000 

84 

351  750  000 

11611 

39 

200  000 

7 

85 

17  320  000 

572 

40 

18  766  000 

620 

86 

46  270  000 

1527 

41 

22  750  '000 

751 

87 

173  750  000 

5734 

42 

75  166  000 

2482 

88 

80  060  000 

2644 

43 

80000 

3 

89 

432  000  000 

14260 

44 

59  425  000 

1963 

90 

1  015  000  000 

33530 

45 

85  300  000 

2817 

91 

6  530  000 

215 

46 

44  716  000 

1476 

91  cans  examined,  3,  or  3.3  percent,  showed  less  than  one  million 
bacteria ;  57  cans,  or  62.6  percent,  showed  between  one  million  and  one 
hundred  million  bacteria ;  and  31,  or  34.1  percent,  showed  over  one 
hundred  million  bacteria. 


1918}  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  231 

If  the  number  of  bacteria  found  in  Can  43  were  added  to  eight 
gallons  of  milk  (the  capacity  of  the  can),  the  germ  content  of  the 
milk  would  be  increased  by  3  bacteria  per  cubic  centimeter;  in  the 
case  of  Can  66  it  would  be  increased  by  1,018,000  bacteria.  If  all  the 
bacteria  found  in  the  91  cans  were  added  to  728  gallons  of  milk  (the 
total  capacity  of  these  cans),  the  germ  content  of  this  milk  would  be 
increased  by  23,523  bacteria  per  cubic  centimeter. 

These  cans  were  inspected  prior  to  the  bacteriological  examination 
and  were  found  to  be  free  from  any  dirt  and  in  most  cases  dry.  It 
is  impossible  to  state  with  certainty  whether  they  were  in  a  better 
or  in  a  worse  condition  than  the  cans  used  for  milk  on  farms  in  gen- 
eral. However,  from  somewhat  extensive  inspection  of  cans  on  a  large 
number  of  farms  and  in  dairies,  the  authors  are  of  the  opinion  that 
these  91  cans  were  cleaner  and  in  a  better  condition  than  the  average 
can  used  for  milk. 

SOURCES  OF  BACTERIA  IN  WASHED  CANS 

The  results  already  presented  show  that  there  are  large  numbers 
of  bacteria  in  freshly  washed  cans,  and  that  in  some  cans  the  num- 
bers are  extremely  large.  Two  of  the  possible  sources  of  these  large 
numbers  of  bacteria  are  the  milk  that  was  previously  in  the  can  and 
the  water  in  which  the  can  was  washed. 

Milk  as  the  Source  of  the  Bacteria 

In  this  experiment  samples  for  bacteriological  study  were  taken 
from  the  milk  of  each  of  153  cans.  The  cans  were  then  emptied  and 
washed  and  the  number  of  bacteria  in  them  was  determined.  The  re- 
sults of  these  examinations  are  given  in  Tables  7,  8,  and  9. 

An  examination  of  these  tables  shows  that  the  germ  content  of  the 
milk  in  the  cans,  as  it  arrived  at  the  dairies,  was  much  higher  in 
Dairy  B  than  in  Dairy  A.  The  number  of  bacteria  in  the  cans  after 
they  were  emptied  and  washed  was  likewise  higher  in  Dairy  B  than 
in  Dairy  A.  When,  however,  the  comparison  is  confined  to  the  in- 
dividual cans  in  the  same  "dairy,  the  relation  between  the  germ  con- 
tent of  the  milk  of  a  given  can  and  the  number  of  bacteria  found  in 
the  can  after  it  was  emptied  and  washed,  is  not  so  evident.  In  a  few 
cases,  as  is  seen  especially  in  the  results  from  the  cans  numbering  85 
to  106,  a  certain  relation  does  exist,  but  in  most  cases  it  is  not  dis- 
cernable. 

How  many  of  the  bacteria  found  in  a  given  washed  can  came  from 
the  milk  held  by  the  can  previous  to  washing  would  naturally  depend 
on  the  germ  content  of  the  milk  and  also  on  the  amount  of  the  milk 
left  in  the  can  after  it  was  washed.  It  is  self  evident  that  after  the 


232 


BULLETIN  No.  204 


[February, 


TABLE  7. — GERM  CONTENT  OF  MILK  IN  THE  CANS,  AND  NUMBER  OF  BACTERIA  IN 

THE  CANS  AFTER  THEY  WERE  WASHED 
(Bacteria  in  cans  determined  by  rinsing  with  one  liter  of  sterile  water) 


No. 

of 
can 

Germ  content 
of  milk  in 
cans,  per  cc. 

No.  of  bacteria 
in  the  can  after 
being  washed 

No. 
of 
can 

Germ  content 
of  milk  in 
cans,  per  cc. 

No.  of  bacteria 
in  the  can  after 
being  washed 

Dairy  A 


1 

380  000 

•  214000000 

21 

1400 

5  900  000 

2 

342  000 

60  000  000 

22 

1100 

5  900  000 

3 

298  000 

2  000  000 

23 

1000 

7  400  000 

4 

175000 

9  000  000 

24 

21200 

2  000  000 

5 

51000 

2  000  000 

25 

10  000 

700  000 

6 

51000 

1  000  000 

26 

8800 

500  000 

7 

48000 

2000000 

27 

7200 

700  000 

8 

13000 

2  O'OO  000 

28 

3600 

2  000  000 

9 

4900 

2  000  000 

29 

2300 

2  600  000 

10 

5300 

5  000  000 

30 

1300 

800  000 

11 

3400 

15  000  000 

31 

1100 

4  900  000 

12 

213  000 

9  000  000 

32 

59800 

3  200  000 

13 

178  000 

8  900  000 

33 

40300 

3  600  000 

14 

176  000 

9  100  000 

34 

23  600 

363  000  000 

15 

152000 

6  800  000 

35 

16700 

9  100  000 

16 

130  000 

3  400  000 

36 

11400 

3  300  000 

17 

18000 

6  300  000 

37 

3600 

7  000  000 

18 

7400 

4  400  000 

38 

1900 

3  200  000 

19 

4-000 

14  300  000 

39 

1800 

4  500  000 

20 

2500 

10  100  000 

40 

1000 

3  800  000 

Dairy  B 

41 

101  300  000 

113  670  000  000 

74 

40000 

430  000  000 

42 

52  000  000 

49  330  000  '000 

75  ' 

2  210  000 

1  690  000  000 

43 

40  800  000 

4  100  000  000 

76 

300  000 

4  440  000  000 

44 

33  500  000 

13  400  000  000 

77 

5520000 

30  400  000  000 

45 

18  170  000 

2  870  000  O'OO 

78 

350  000 

18  650  000  000 

46 

18  000  000 

6  060  000  000 

79 

10  830  000 

5  670  000  000 

47 

13  200  000 

7  970  000  000 

80 

14  500  000 

8  400  000  000 

48 

9  370  000 

930  000  OO'O 

81 

2  750  000 

70  660  000  000 

49 

6  920  000 

4  900  000  000 

82 

1  390  000 

104  330  000  000 

50 

6  600  000 

2  220  000  000 

83 

290  000 

21  800  000  000 

51 

5  460  000 

8  000  000  000 

84 

9  500  000 

720  000  000 

52 

5  270  000 

330  000  000 

85 

10000 

140  000  000 

53 

4530000 

51  330  000  000 

86 

550  000 

1  200  000  000 

54 

4  490  000 

1  660  000  000 

87 

1  970  000 

26  970  000  000 

55 

3  950  000 

3  160  000  000 

88 

710  000 

4  680  000  000 

56 

3  400  000 

40  000  000  000 

89 

350  000 

12  600  000  000 

57 

3  000  000 

690  000  000 

90 

20000 

3  890  000  000 

58 

2  960  000 

62  060  000  000 

91 

650  000 

18  920  000  000 

59 

2  460  000 

47  000  000  000 

92 

10000 

200  000  000 

60 

2  010  000 

9  470  000  000 

93 

1  500  000 

19  070  000  000 

61 

1  990  000 

7  600  000  000 

94 

220  000 

3  460  000  000 

62 

1  820  000 

650  000  000 

95 

40000 

130  000  000 

63 

1  000  000 

5270-000000 

96 

900  000 

26  240  000  000 

64 

910  000 

9  400  000  000 

97 

510  000 

5080000000 

65 

800  000 

110000000 

98 

170  000 

2  080  000  000 

66 

620  000 

43  000  000  000 

99 

10000 

190  000  000 

67 

510  000 

4  300  000  000 

100 

130  000 

1  580  000  000 

68 

340  000 

2  130  000  000 

101 

11500000 

65  000  000  000 

69 

320  000 

11  470  000  000 

102 

2  060  000 

21  660  000  000 

70 

230  000 

5  270  000  000 

103 

60000 

650  000  000 

71 

160  000 

3  070  000  000 

104 

420  000 

16  400  000  000 

72 

70000 

920  000  000 

105 

2  000  000 

40  330  000  000 

73 

70  000 

250  000  000 

106 

40000 

270  000  000 

1918]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  233 

can  is  emptied  and  washed,  the  amount  of  the  milk  still  adhering  to 
the  walls  of  the  can  is  extremely  small.- 

That  the  milk  held  by  a  can  previous  to  washing  was  not  the  prin- 
cipal source  of  the  bacteria  in  the  washed  cans  in  cases  where  the  num- 
ber of  bacteria  was  large,  may  be  shown  by  calculating  the  amount 
of  the  milk  that  would  have  been  necessary  to  have  supplied  the  num- 
ber of  bacteria  found  in  the  washed  cans.  Cans  65  and  66  may  be 
taken  for  this  calculation.  These  two  cans  were  washed  in  succession, 
within  one  minute  of  each  other,  in  the  same  wash  water.  The  germ 
content  of  the  milk  held  by  Can  65  wras  800,000  bacteria  per  cubic 
centimeter,  and  the  number  of  bacteria  in  this  can  after  it  was  washed 
was  110,000,000.  it  would  have  required  137  cc.  of  the  milk  to  have 
supplied  the  number  of  bacteria  found  in  the  can  after  it  was  washed. 
The  germ  content  of  the  milk  in  Can  66  was  620,000  bacteria  per  cubic 
centimeter,  and  after  the  can  was  washed  the  number  of  bacteria  found 
in  it  was  43,000,000,000.  In  this  case  it  would  have  required  69,355 
cc.  (about  18  gallons)  of  the  milk  to  have  supplied  this  number  of 
bacteria. 

It  is  seen  from  this  experiment,  therefore,  that  in  dairies  which 
receive  milk  with  high  germ  content,  the  cans  after  being  washed,  and 
if  not  steamed,  will  have  correspondingly  large  numbers  of  bacteria. 
On  the  other  hand,  the  large  numbers  of  bacteria  in  some  cans  after 
they  are  washed  in  the  same  dairy  and  in  the  same  lot  of  wash  water, 
must  have  some  source  other  than  the  milk. 

Wash  Water  as  a  Source  of  Bacteria 

When  milk  is  poured  from  a  can,  a  small  amount  of  it  always  ad- 
heres to  the  inner  walls  of  the  can.  In  the  process  of  washing,  these 
traces  of  milk  are  transferred  to  the  wash  water.  It  is  evident  that 
the  germ  content  of  the  wash  water  may  become  very  high  if  the  milk 
was  heavily  seeded  with  bacteria,  if  the  cans  are  dirty,  or  if  a  large 
number  of  cans  are  washed  in  the  same  lot  of  wash  water.  This  ex- 
periment was  therefore  undertaken  to  determine  the  influence*  of  the 
wash  water  on  the  number  of  bacteria  in  the  washed  cans. 

All  the  cans  reported  in  Table  8  were  washed  in  one  lot  of  wash 
water,  and  the  same  was  true  of  those  listed  in  Table  9.  In  Tables  10 
and  11  a  fresh  lot  of  water  was  used  for  every  set  of  cans,  each  set 
including  from  five  to  nine  cans. 

In  Table  8  the  wash  water  contained  one  percent  of  sodium-car- 
bonate washing  powder.  In  Table  9  the  wash  water  contained  no 
washing  powder  of  any  kind.  In  Table  }0  each  set  of  cans  was  washed 
first  in  one-percent  washing-powder  solution  and,  without  using  these 
cans  for  milk  after  this  washing,  they  were  washed  again  thirty  min- 
utes later  but  only  in  plain  water.  In  Table  11  the  cans  were  treated 
exactly  as  in  Table  10  except  that  the  first  washing  was  done  in  plain 


234 


BULLETIN  No.  204 


[February, 


water  and  the  second  washing  in  one-percent  solution  of  washing 
powder. 

In  Tables  8  and  9  the  samples  for  bacteriological  study  were  taken 
from  the  milk  of  each  can  just  before  the  cans  were  emptied  and 
washed.  The  samples  from  the  wash  water  were  taken  from  the  vat : 
first,  at  the  beginning  of  washing ;  second,  at  certain  intervals  during 
the  washing;  and  third,  after  all  the  cans  were  washed.  In  Tables 
10  and  11,  the  milk  samples  were  omitted,  and  the  samples  from  the 
wash  water  in  the  vat  were  taken  at  the  beginning  and  at  the  end  of 
the  washing  of  each  set  of  cans. 

TABLE  8. — GERM  CONTENT  OF  MILK,  OP  WASH  WATER,  AND  OP  WASHED  CANS 
(Cans  washed  in  25  gallons  of  water,  with  washing  powder:    Dairy  B) 


No. 
of 
can 

Germ  content 
of  milk  in 
cans,  per  ce. 

Bacteria  removed  from 
washed  cans  by  one 
liter  of  rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Before  washing 


100  000 


1 

2210000 

1  690  000  000 

2 

300  000 

4  440  000  000 

3 

5  520  000 

30  400  000  000 

4 

350  000 

•   18  650  000  000 

5 

10  830  000 

5  670  000  000 

6 

14  500  000 

8  400  000  000 

7 

2  750  000 

70  660  000  000 

8 

1  390  000 

104  330  000  000 

9 

290  000 

21  800  000  000 

10 

9  500  000 

720  000  000 

11 

10000 

140  000  000 

12 

550  000 

1  200  000  000 

After  12  cans  were  washed 


3  210  000 


13 

1  970  000 

26  970  000  000 

14 

710  000 

4  680  000  000 

15 

350  000 

12  000  000  000 

16 

20000 

3  890  000  000 

17 

650  000 

18  920  000  000 

18 

10000 

200  000  000 

19 

1  500  000 

19  070  000  000 

20 

220  000 

3  460  000  000 

21* 

40000 

130  000  000 

22 

900  000 

26  240  000  000 

After  22  cans  were  washed                         3  420  000 

23 

510  000 

5  080  000  000 

24 

170  000 

2  080  000  000 

25 

10000 

190  000  000 

26 

130  000 

1  580  000  000 

27 

11500000 

65000000000  - 

28 

2  060  000 

21  660  000  000 

29 

60000 

650  000  000 

30 

420  000 

16  400  000  000 

31 

2  000  000 

40  330  OCO  000 

32 

40  000 

270  000  000 

After  32  cans  were  washed 


5  100  000 


1918} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


235 


After  each  can  was  washed  it  was  allowed  to  stand  twenty  to 
thirty  minutes;  then  one  liter  of  sterile  water  was  poured  in  and 
after  thoro  shaking,  the  germ  content  of  this  water  was  determined. 
In  Tables  10  and  11  each  can  was  washed  twice  in  succession  and  the 
number  of  bacteria  determined  after  each  washing. 

All  the  cans  in  Tables  8  and  9,  those  in  Table  10  numbering  21  to 
43,  and  those  in  Table  11  numbering  27  to  44  came  from  Dairy  B. 
The  remaining  cans  in  Tables  10  and  11  came  from  Dairy  A.  For 
the  purpose  of  this  experiment,  however,  the  usual  methods  of  wash- 
ing followed  in  these  dairies  were  discarded  and  the  cans  in  both 
dairies  were  washed  "in  the  same  way.  About  25  gallons  of  warm 
water  was  run  into  the  vat,  and  when  washing  powder  was  used,  one 
percent  of  it  was  added  to  the  water.  Each  can  was  placed  in  the 
water,  scrubbed  with  a  brush,  and  then  inverted  on  a  rack  for  about 
six  seconds  to  drain.  None  of  the  cans  in  either  dairy  were  rinsed 
with  plain  water  after  being  washed. 

The  germ  content  of  the  water  supply  in  these  dairies  varied  from 
100  to  2,000  bacteria  per  cubic  centimeter.  It  will  be  noticed  from 
the  above  tables  that  when  the  water  was  run  into  the  vat  preparatory 
to  being  used  for  washing  the  cans,  its  germ  content  invariably  in- 
creased. For  example,  in  Table  8  before  any  cans  were  washed  in 
the  water  the  germ  content  was  100,000  bacteria  per  cubic  centimeter. 
This  increase  was -apparently  due  to  the  bacteria  present  on  the  inner 
surface  of  the  vat. 

TABLE  9. — GERM  CONTENT  OF  MILK,  OF  WASH  WATER,  AND  OF  WASHED  CANS 
(Cans  washed  in  25  gallons  of  water,  without  washing  powder:    Dairy  B) 


No. 
of 
can 

Germ  content 
of  milk  in 
cans,  per  cc. 

Bacteria  removed  from 
washed  cans  by  one 
liter  of  rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Before  any  cans  were  washed                          155  000 

33 
34 
35 
36 
37 
38 
39 
40 
41 

3  060  000 
520  000 
130  000 
1  390  000 
1  870  000 
105  000  000 
640  000 
11  600  000 
940  000 

480  000  000 
1  900  000  000 
1  180  000  000 
170  000  000 
8  750  000  000 
10  970  000  000 
820  000  000 
710  000  000 
50  000  000 

After  9  cans  were  washed                             412  000 

42 
43 

44 
45 
46 

47 

80000 
80000 
900  000 
830  000 
50000 
6  300  000 

720  000  000 
490  €00  000 
1  170  000  000 
.  10000000 
280  000  000 
14  690  000  000 

After  15  cans  were  washed                          457  000 

236 


BULLETIN  No.  204 


[February, 


TABLE  10. — GERM  CONTENT  OF  WASH  WATER  AND  OF  CANS  WASHED  TWICE  IN 

SUCCESSION;    FIRST  IN  WASHING-POWDER  SOLUTION,  THEN  IN  PLAIN  WATER 

(New  lot  of  25  gallons  of  water  used  for  every  5  to  9  cans) 


No. 
of 
can 

First  washing  —  washing  powder 

Second  washing  —  plain  water 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  ee. 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Dairy  A 

Before  washing                                       500                                                    15400 

1 
2 
3 
4 
5 

7  000  000 
24  000  000 
17  000  000 
1  000  000 
3  000  000 

500  000 
400  000 
100000 
100  000 

After  5  cans  were  washed               14  200                                                    44  400 

Before  washing                                  28000                                                      5600' 

6 
7 
8 
9 
10 
11 
12 
13 
14 

2  000  000 
3  000  000 
3  000  000 
2  000  000 
2  000  000 
2  000  000 
2  000  000 
47  000  000 
2  000  000 

- 

400  000 
400  000 
300  000 
900  000 
600  000 
500  000 
900  000 
10  600  000 
600  000 

After  9  cans  were  washed               88  000                                                    28  000 

Before  washing                                  21  800                                                      7  500 

15 
16 
17 
18 
19 
20 

500  000 
700  000 
600  000 
700  000 
1  600  000 
700  000 

490  000 
600  000 
900  000 
410  000 
640  000 
620  000 

After  6  cans  were  washed                40  000                                                    47  000 

Dairy  B 

Before  washing                                  28  000                                                     17  000 

21 
22 
23 
24 
25 

190  000  000 
100  000  000 
3  190  000  000 
10  400  000  000 
240  000  000 

30  900  000 
20  100  000 
723  000  000 
787  000  000 
14  600  000 

After  5  cans  were  washed        20  000  000                                                1  400  000 

Before  washing                                   30000                                                         7000 

26 
27 
28 
29 
30 

10  000  000 
60  000  000 
60  000  000 
160  000  000 
1  450  000  000 

100  000 
2  600  000 
2  300  000 
3  800  000 
30  800  000 

After  5  cans  were  washed             670  000                                                   110  000 

1918] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


237 


TABLE  10. — Concluded 


No. 

of 
can 

First  washing  —  washing   powder 

Second  washing  —  plain  water 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Before  washing 


20500 


5500 


31 
32 
33 
34 
35 

58  000  0-00 
1  023  000  000 
777  000  000 
98  000  000 
28  000  000 

6  400  000 
260  000  000 
97  000  000 
25  000  000 
2  400  000 

After  5  cans  were  washed     400  000                    140  000 

Before  washing              19  000                      18  200 

36 

37 
38 
39 
40 
41 
42 
43 

40  000  000 
3  000  000 
5  700  000  000 
753  000  000 
194  000  000 
1  153  000  000 
4  400  000  000 
173  000  000 

17  600  000 
1  000  000 
2  830  000  000 
96  600  000 
11  000  000 
250  000  000 
1  066  600  000 
10  100  000 

After  8  cans  were  washed   14  000  000                    450  000 

As  the  process  of  washing  proceeded,  the  number  of  bacteria  in 
the  wash  water  always  increased.  The  thirty-two  cans  recorded  in 
Table  8  were  washed  in  water  containing  one  percent  of  washing 
powder.  Before  any  cans  were  washed,  the  water  had  100,000  bacteria 
per  cubic  centimeter.  After  12  cans  were  washed,  the  germ  content 
of  the  water  increased  to  3,210,000  bacteria;  after  22  cans  were 
washed  it  increased  to  3,420,000;  and  after  32  cans  were  washed  it 
became  5,100,000.  The  water  in  which  the  cans  in  Table  9  were  washed 
contained  no  washing  powder.  Its  initial  germ  content  was  155,000 
bacteria  per  cubic  centimeter,  and  after  15  cans  were  washed  in  it, 
its  germ  content  increased  to  457,000  bacteria.  Similar  results  were 
obtained  in  Tables  10  and  11,  where  a  new  lot  of  wash  water  was 
prepared  for  every  five  to  nine  cans.  In  one  case  the  initial  germ 
content  of  the  wash  water  was  28,000  bacteria  per  cubic  centimeter, 
and  after  5  cans  were  washed,  its  germ  content  increased  to  20,000,000 
bacteria. 

The  number  of  bacteria  added  to  the  cans  by  the  wash  water  de- 
pends naturally  on  the  germ  content  of  the  water  and  also  on  the 
amount  of  the  water  left  in  the  cans.  Several  trials  on  this  point 
demonstrated  that  from  10  to  25  cc.  of  water  adhere  to  the  inner 
surface  of  a  can. 


238 


BULLETIN  No.   204 


[February, 


TABLE  11. — GERM  CONTENT  OF  WASH  WATER,  AND  OP  CANS  WASHED  TWICE  IN 

SUCCESSION  ;    FIRST  IN  PLAIN  WATER,  THEN  IN  WASHING-POWDER  SOLUTION 

(New  lot  of  25  gallons  of  water  used  for  every  5  to  9  cans) 


No. 
of 
can 

First  washing  —  plain  water 

Second  washing  —  washing  powder 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  cc. 

Dairy  A 

Before  washing                                       400                                                       13  200 

1 

2 
3 
4 
5 

340  000  000 
1  000  000 
2  000  000 

277  ooo  ooo 

4  000  000 

\ 

100  000 
7  000  000 
4  000  000 

After  5  cans  were  washed               11  800                                                    47  600 

Before  washing                                       500                                                       15  400 

6 
7 
8 
9 

10 

7  000  000 
24  000  000 
17000000 
1  000  000 
3  000  000 

500  000 
400  000 
100  000 
100  000 

After  5  cans  were  washed               14  200                                                    44  400 

Before  washing                                     1  400                                                         3  300 

11 
12 
13 

14 
15 
16 
17 
18 
19 

1  000  000 
7  000  000 
14  000  000 
3  000  000 
2  000  000 
1  000  000 
2  000  000 
5  000  000 
232  000  000 

800  000 
7  000  000 
300  000 
800  000 
700  000 
1  0-00  000 
1  700  000 
1  300  000 
17  900  000 

After  9  cans  were  washed             200  000                                                       94  000 

Before  washing                                 12  900                                                      6  100 

20 
21 
22 
23 
24 
25 
26 

9  000  000 
1  000  000 
1  100  000 
1  200  000 
1  300  000 
400  000 
1  200  000 

• 

620  000 
580  000 
620  000 
770  000 
700  000 
790  000 
830  000 

After  7  cans  were  washed               09  000                                                        

1018] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


239 


TABLE  11. — Concluded 


No. 
of 
can 

First  washing  —  plain  water 

Second  washing  —  washing  powder 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  ce. 

Bacteria  removed 
from  washed  cans 
by  one  liter  of 
rinse  water 

Germ  content  of 
wash  water, 
per  ce. 

Dairy  B 


Before  washing              200 

27 

3  350  000  000 

115  200  000 

28 

970  000  000 

23  700  000 

29 

3  630  000  000 

143  300  000 

30 

140  000  000 

9  600  000 

31 

450  000  000 

500  000 

After  5  cans  were  washed    4  800  000                    510  000 

Before  washing               1  400                      28  000 

32 

1  084  000  000 

783  000  000 

33 

11  000  '000 

2  700  000 

34 

3  416  000  000 

355  000  000 

35 

132  000  000 

82  000  000 

36 

26  000  000 

9  800  000 

After  5  cans  were  washed    1  200  000                    600  000 

Before  washing              107  000 

37 

37  000  000 

82  700  000 

38 

55  000  000 

66  000  000 

39 

184  000  000 

64  700  000 

40 

748  000  000 

123  300  000 

41 

33  000  000 

10  300  000 

42 

563  000  000 

100  300  000 

43 

25  000  000 

22  000  000 

44 

47  000  000 

14  800  000 

After  8  cans  were  washed   14  400  000                     450  000 

'Cans  31  and  32  in  Table  8  were  washed  in  the  same  water  within 
one  minute  of  each  other.  In  Can  31  the  bacteria  numbered  40,330,- 
000,000  and  in  Can  32,  270,000,000.  The  germ  content  of  the  wash 
water  at  this  point  was  5,100,000  bacteria  per  cubic  centimeter. 
If  the  number  of  bacteria  in  these  two  cans  was  due  to  the  wash 
water  alone,  it  would  have  required  53  cc.  of  the  water  to  have  sup- 
plied the  number  in  Can  32,  while  in  Can  31  it  would  have  required 
7,907  cc.  of  the  water.  Similar  calculations  for  each  can  in  these 
tables  show  that  in  some  cans  the  relatively  small  numbers  of  bacteria 
correspond  somewhat  closely  to  the  number  of  bacteria  in  the  amount 
of  the  water  that  may  adhere  to  them.  However,  in  many  of  the  cans 
the  number  is  too  large  to  be  accounted  for  by  the  wash-water  con- 
tamination alone.  In  addition,  there  appears  to  be  no  gradual  in- 
crease in  the  germ  content  of  the  consecutively  washed  cans.  This 
leads  to  the  conclusion,  therefore,  that  the  exceptionally  large  numbers 


240  BULLETIN  No.  204  [February, 

of  bacteria  in  the  washed  cans  had  some  other  source  than  the  wash 
water. 

In  1889  Conn  stated  that  ''bacteria  gather  upon  the  sides  of  the 
utensils  and  develop  in  the  minute  portions  of  milk,  grease,  and  other 
matter  from  which  it  is  difficult  to  free  the  vessels  completely  by 
washing."  The  data  in  this  experiment  support  Conn's  conclusion 
and  further  emphasize  the  striking  capacity  of  the  bacteria  to  mul- 
tiply in  the  extremely  minute  portions  of  the  milk,  fat,  and  other 
matter,  and  to  adhere  to  the  walls  of  the  cans.  The  large  numbers  of 
bacteria  found  in  cans  may  be  accounted  for  on  the  ground  that  the 
cans  are  difficult  to  clean  thoroly,  and  that  in  the  traces  of  this  dirt 
numerous  bacteria  are  imbedded  and  then  are  loosened  by  the  washing 
process  and  subsequently  removed  by  rinsing. 

The  purpose  of  this  experiment  was  also  to  show  the  influence  of 
the  washing  powder  upon  the  germ  content  of  the  wash  water  and 
the  washed  cans.  The  cans  listed  in  Table  8  were  washed  in  water 
containing  washing  powder  and  those  in  Table  9  in  plain  water.  Those 
shown  in  Tables  10  and  11  were  washed  twice  in  succession,  half  of 
them  in  washing-powder  solution  first  and  then  in  plain  water,  and 
half  in  plain  water  first  and  then  in  washing-powder  solution.  A 
perusal  of  these  tables  shows  that  the  washing  powder  exerted  no  dis- 
cernable  influence  upon  the  germ  content  of  the  wash  water  or  of  the 
washed  cans.  The  germ  content  of  the  wash  water  increased  during 
the  washing  process  to  about  the  same  extent  in  the  plain  water  and 
in  the  washing-powder  solution,  and  many  of  the  cans  in  both  cases 
had  extremely  large  numbers  of  bacteria'. 

It  is  customary  in  some  dairies  to  wash  a  large  number  of  uten- 
sils in  the  same  lot  of  wash  water,  and  then  not  to  rinse  them  suffi- 
ciently with  clean  water  or  not  to  rinse  them  at  all.  Such  practice 
results  in  seeding  the  wash  water  with  large  numbers  of  bacteria  which 
were  present  in  the  dirt  and  in  the  milk  that  adhere  to  the  walls  of 
the  utensils.  When  utensils  are  washed  in  such  a  manner,  some  may 
contain  a  larger  number  of  bacteria  after  they  are  washed  than  they 
contained  before  they  were  washed. 

Naturally  the  object  of  the  washing  process  is  to  remove  the  dirt 
and  the  milk  residues  from  the  can,  and  the  completeness  with  which 
it  accomplishes  this  result  is  the  true  measure  of  its  success.  A  re- 
duction of  the  germ  life  in  the  can  is  ordinarily  accomplished  at  the 
same  time,  but  this  reduction  cannot  be  carried  to  satisfactory  limits 
by  the  washing  process  without  an  undue  expense  for  water,  heat,  and 
washing  powder.  The  destruction  of  the  germ  life  in  the  cans  is 
ordinarily  accomplished  more  economically  and  more  completely  by 
the  direct  application  of  steam. 


1918]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  241 

BACTERIA  FOUND  IN  BOTTLES  FRESHLY  WASHED  AND  IN  BOTTLES 
STANDING  TWENTY-FOUR  HOURS 

^ 

The  washing  of  milk  bottles  is  in  a  measure  comparable  to  that 
of  cans.  Like  cans,  the  bottles  are  washed  in  the  same  water  in  large 
numbers.  They  are  returned  to  the  dairy  at  times  in  dirty  condition 
and  frequently  contain  traces  of  milk  with  high  germ  content: 

In  the  dairy  in  which  this  experiment  was  conducted,  it  was  the 
custom  to  wash  from  150  to  200  bottles  in  a  vat  containing  about  60 
gallons  of  warm  water  to  which  was  added  5  pounds  of  sodium-car- 
bonate washing  powder.  The  bottles  were  scrubbed  with  a  steam- 
driven  brush,  and  then  rinsed  in  another  vat  containing  about  60 
gallons  of  tap  water;  they  were  not  steamed.  For  the  purpose  of 
this  experiment  two  sets  of  the  washed  bottles,  nine  to  fourteen  in 
each  set,  were  selected  from  each  of  fourteen  different  lots  for  study. 

In  order  to  obtain  two  comparable  sets  of  bottles,  selection  was 
made  in  the  following  manner:  The  first  two  bottles  washed  were 
taken,  then  the  eleventh  and  twelfth,  then  the  twenty -first  and  twenty- 
second,  and  so  on  until  all  the  bottles  were  washed.  Those  having  odd 
numbers  constituted  the  first  set  and  those  with  even  numbers  the 
second  set.  The  bottles  in  the  first  set  were  examined  immediately 
after  being  washed  and  those  in  the  second  set  after  they  had  been 
kept  inverted  twenty-four  hours  on  a  wire  rack.  The  examination 
consisted  in  rinsing  each  bottle  with  100  cc.  of  sterile  water  and  de- 
termining the  number  of  bacteria  in  the  water.  The  results  of  the 
examination  of  308  bottles  are  given  in  Table  12. 

The  number  of  bacteria  found  in  these  bottles  was  variable  and  in 
some  cases  large.  Among  the  bottles  examined  immediately  after 
washing  25,  or  16.2  percent,  had  more  than  one  million  bacteria,  and 
129,  or  83.8  percent,  had  less  than  one  million.  The  largest  number  of 
bacteria  found  in  any  one  bottle  was  40,660,000,  and  the  smallest  was 
20,000. 

The  bottles  that  were  held  twenty-four  hours  after  they  were 
washed  were  found  to  be  dry  and  free  from  bad  odors.  Eighty-four  of 
these,  or  54.5  percent,  had  more  than  one  million  bacteria,  and  70,  or 
45.5  percent,  had  less  than  one  million.  The  largest  number  of  bacteria 
found  was  231,700,000,  and  the  smallest  number  was  3,000. 

'  It  will  be  observed  that  some  of  the  bottles  examined  immediately 
after  they  were  washed  had  a  larger  number  of  bacteria  than  some  of 
the  bottles  held  twenty-four  hours.  On  the  average,  however,  there 
was  a  decided  increase  in  the  number  of  bacteria  in  the  bottles  which 
were  held  twenty-four  hours.  This  is  brought  out  more  clearly  by 
calculating  the  average  number  of  bacteria  per  bottle  on  each  of  the 
different  days/-  These  averages  are  given  in  Table  13. 

The  averages  in  Table  13  show  that,  in  all  cases,  the  set  of  bottles 
held  twenty-four  hours  averaged  more  bacteria  than  the  corresponding 


242 


BULLETIN  No.  204 


[February, 


TABLE  12. — NUMBER  OF  BACTERIA  IN  BOTTLES  FRESHLY  WASHED.  AND  TWENTY-FOUR 

HOURS  LATER:    DAIRY  A 
(As  determined  by  rinsing  each  bottle  with  100  cc.  of  sterile  water)   * 


Total  number  of  bacteria  in  bottles  — 

Total  number  of  bacteria  in  bottles  — 

No.  of 

Freshly 

No.  of 

24  hours  after 

No.  of 

Freshly 

No.  of 

24  hours  after 

bottle 

washed 

bottk 

washing 

bottle 

washed 

bottle 

washing 

June  20 

June  20-21 

June  21 

June  21-22 

1 

3  800  000 

2 

47  000  000 

25 

110  000 

26 

3  040  000 

3 

6  000  000 

4 

68  300  000 

27 

110  000 

28 

36  500  000 

5 

5  200  00€ 

6 

120  000  000 

29 

140  000 

30 

61  330  000 

7 

4  700  000 

8 

123  000  000 

31 

110  000 

32 

11  800  000 

9 

4  300  000 

10 

107000000 

33 

90000 

34 

48  670  000 

11 

4  500  000 

12 

15  500  000 

35 

-  120000 

36 

22330000 

13 

15  000  000 

14 

36  000  000 

37 

110  000 

38 

29  330  000 

15 

7  900  000 

16 

231  700  000 

39 

490  000 

40 

36  330  000 

17 

6  100  000 

18 

18  700  000 

41 

140  000 

42 

68  000  000 

19 

11  300  000 

20 

64  600  000 

43 

40  660  000 

44 

72  330  000 

21 

8  000  000 

22 

27  700  000 

23 

6  600  000 

24 

163  000  000 

June  22 

June  22-23  , 

June  23 

June  23-24 

45 

2  950  000 

46 

4  700  000 

63 

30000 

64 

2  290  000 

47 

100  000 

48 

100  000 

65 

2  730  000 

66 

1  280  000 

49 

340  000 

50 

5  130  000 

67 

40000 

68 

6  030  000 

51 

520  000 

52 

15  430  000 

69 

200  000 

70 

15  000  000 

53 

110  000 

54 

6  570  000 

71 

70000 

72 

8  570  000 

55 

270  000 

56 

20  670  000 

73 

120  000 

.74 

9  870  000 

57 

850  000 

58 

5  400  000 

75 

190  000 

76 

34  000  000 

59 

210  000 

60 

910  000 

77 

80000 

78 

1  830  000 

61 

780  000 

62 

180  000 

79 

100  000 

80 

3  190  000 

June  26 

June  26-27 

June  27 

June  27-28 

81 

630  000 

82 

360  000 

101 

43000 

102 

30000 

83 

410  000 

84 

30  500  000 

103 

315  000 

104 

2  700  000 

85 

320  000 

86 

430  000 

105 

83000 

106 

480  000 

87 

340  000 

88 

300  000 

107 

68000 

108 

210  000 

89 

760  000 

90 

30000 

109 

40000 

110 

10000 

91 

400  000 

92 

120  000 

111 

335  000 

112 

470  000 

93 

230  000 

94 

170  000 

113 

54000 

114 

160  000 

95 

590  000 

96 

140  000 

115 

48000 

116 

10000 

97 

250  000 

98 

350  000 

117 

303  000 

118 

1  490  000 

99 

220  000 

100 

120  000 

119 

71000 

120 

2  020  000 

June  28 

June  28-29 

June  30 

June  30  — 

July  1 

121 

62000 

122 

370  000 

139 

305  000 

140 

830  000 

123 

295  000 

124 

80000 

141 

243  000 

142 

1  920  000 

125 

175  000 

126 

140  000 

143 

279  000 

144 

10000 

127 

901  000 

128 

230  000 

145 

30000 

146 

750  000 

129 

170  000 

130 

100  000 

147 

600  000 

148 

2  070  000 

131 

220  000 

132 

15  160  000 

149 

61000 

150 

630  000 

133 

333  000 

134 

80000 

151 

2  430  000 

152 

470  000 

135 

5  733  000 

136 

1  500  000 

153 

93  000- 

154 

250  000 

137 

1  130  000 

138 

90000 

155 

41000 

156 

320  000 

157 

61000 

158 

260  000 

ISIS] 


GERM  CONTEXT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


243 


TABLE  12. — Concluded 


Total  number  of  bacteria  in  bottles- 

Total  number  of  bacteria  in  bottles  — 

No,  of 

Freshly 

No.  of 

24  hours  after 

No.  of 

Freshly 

No.  of 

24  hours  after 

bottle 

washed 

bottle 

washing 

bottle 

washed 

bottle 

washing  • 

Sept.  25, 

Sept.  25-26, 

Sept.  25, 

Sept.  25-26, 

a.  m. 

a.  m. 

p.  m. 

p.  m. 

159 

450  000 

160 

90000 

183 

43000 

184 

13  330  000 

161 

36000 

162 

3000 

185 

46000 

186 

1  926  000 

163 

40000 

164 

3  090  000 

187 

66000 

188 

2  826  000 

165 

26000 

166 

853  000 

189 

36000 

190 

3  026  000 

167 

50000 

168 

3000 

191 

66000 

192 

310  000 

169 

50000 

170 

250  000 

193 

43000 

194 

310  000 

171 

63000 

172 

43000 

195 

33000 

196 

930  000 

173 

36000 

174 

660  000 

197 

50000 

198 

350  000 

175 

40000 

176 

76000 

199 

30  000 

200 

630  000 

177 

.  53000 

178 

396  000 

201 

740  000 

202 

316  000 

179 

66000 

180 

1  300  000 

203 

66000 

204 

2  773  000 

181 

20000 

182 

206  000 

205 

80000 

206 

150  000 

Sept.  27, 

Sept,  27-28, 

Sept.  27, 

Sept.  37-28, 

a.  m. 

a.  m. 

p.  m. 

p.  m. 

207 

83000 

208 

4  880  000 

231 

340  000 

232 

4  560  000 

209 

593  000 

210 

4  800  000 

233 

350  000 

234 

3  746  000 

211 

90000 

212 

110  000 

235 

540  000 

236 

5  300  000 

213 

276  000 

214 

4  226  000 

237 

396  000 

238 

11  400  000 

215 

276  000 

216 

4073000 

239 

1  553  000 

240 

6  933  000 

217 

283  000 

218 

8  600  000 

241 

300  000 

242 

1  753  000 

219 

110  000 

220 

313  000 

243 

740  000 

244 

3  700  000 

221 

100  000 

222 

320  000 

245 

540  000 

246 

2  950  000 

223 

163  000 

224 

13000 

247 

370  000 

248 

13  660  000 

225 

2  493  000 

226 

3  396  000 

249 

660  000 

250 

10  300  000 

227 

363  000 

228 

6000 

251 

1  043  000 

252 

1  336  000 

229 

570  000 

230 

660  000 

253 

1  090  000 

254 

12  330  000 

Sept.  2?, 

Sept.  29-30, 

Oct.  2,  p.  m. 

Oct.  2-3,  p.m. 

a.  m. 

a.  m. 

255 

6  986  000 

256 

6  400  000 

285 

73000 

286 

50000 

257 

280  000 

258 

9  530  000 

287 

57000 

288 

10000 

259 

3  160  000 

260 

2  670  000 

289 

99000 

290 

60000 

261 

450  000 

262 

2  100  000 

291 

77000 

292 

10  720  000 

263 

340  000 

264 

6  020  000 

293 

165000 

294 

80000 

265 

436  000 

266 

3  995  000 

295 

237  000 

296 

30  00.0 

267 

230  000 

268 

2  600  000 

297 

63000 

298 

110  000 

269 

513  000 

270 

4  606  000 

299 

46000 

300 

10000 

271 

253  000 

272 

3  853  000 

301 

44000 

302 

2  020  000 

273 

8  700  000 

274 

4  253  000 

303 

56000 

304 

270  000 

275 

350  000 

276 

3366000 

305 

74000 

306 

260  000 

277 

286  000 

278 

1  963  000 

307 

64000 

308 

110  000 

279 

400  000 

280 

60000 

281 

386  000 

282 

3000 

283 

296  000 

284 

26000 

244 


BULLETIN  No.  204 


[February, 


set  of  the  same  day  examined  immediately  after  the  washing.  The 
average  number  of  bacteria  in  all  the  154  bottles  examined  immediately 
after  the  washing  was  1,271,950  per  bottle,  and  in  those  held  twenty- 
four  hours  it  was  12,283,490  per  bottle. 

One  quart  is  approximately  950  cubic  centimeters ;  so  that  if  these 
bottles  had  been  filled  with  milk,  the  germ  content  of  the  milk  would 
have  been  increased,  on  the  average,  by  1,339  bacteria  per  cubic  centi- 
meter by  the  freshly  washed  bottles  and  12,930  bacteria  per  cubic 
centimeter  by  the  bottles  held  twenty-four  hours  after  the  washing. 
From  these  results  it  is  evident  that  bottles  washed  but  not  steamed 
may  have  an  appreciable  effect  upon  the  germ  content  of  milk,  espe- 
cially when  they  are  held  for  some  hours  before  being  filled. 

TABLE  13. — AVERAGE  NUMBER  OF  BACTERIA  IN  WASHED  BOTTLES 


Date, 

Number  of 

Bottles  freshly 

Bottles  held  24  hours 

1916 

bottles 

washed 

after  washing 

June 

20 

12 

6  950  000 

85  200  000 

21 

10 

4  208  000 

38  966  000 

22 

9 

681  000 

6  565  000 

23 

9 

395  000 

9  115  000 

26 

10 

415  000 

3  252  000 

27 

10 

136  000 

758  000 

28 

9 

1  002  000 

1  970  000 

30- 

10 

414  000 

751000 

Sept. 

25  a.m. 

12 

78  OOO' 

581000 

25  p.m. 

12 

108  000 

2  240  000 

27  a.m. 

12 

450  000 

2  616  000 

27  p.m. 

12 

660  000 

6  497  000 

29  a.m. 

15 

1  538  000 

3  429  000 

Oct. 

2.  p.m. 

12 

879  000 

1  144  000 

Average  number  of  bacteria 

in  154  bottles.  . 

1  271  950 

12283490 

1918}  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  245 

PART    II.— INFLUENCE     SHOWN    BY    EXAMINATION    OF 

THE  MILK 

The  four  experiments  reported  in  this  part  were  designed  to  ascer- 
tain the  influence  of  the  various  unsteamed  utensils  upon  the  germ 
content  of  milk,  in  actual  dairy  operations.  This  influence  was 
measured  by  the  difference  in  the  germ  content  of  milk  handled  in 
steamed  and  in  unsteamed  utensils. 

The  utensils  were  washed  as  described  on  page  219.  The  steaming 
consisted  in  holding  the  utensils  in  a  chamber  filled  with  flowing 
steam,  for  about  an  hour,  with  the  exception  that  some  of  the  pails 
and  cans  were  held  over  a  jet  of  steam  for  two  to  three  minutes.  The 
thoroness  of  the  steaming  of  the  utensils  was  always  tested  bacteriolog- 
ically  and  found  to  be  satisfactory. 

COLLECTIVE  INFLUENCE  OF  UTENSILS  AT  THE  BARN 

This  experiment  was  designed  to  measure  the  collective  influence 
on  the  germ  content  of  milk  of  unsteamed  pails,  strainers,  and  cans 
used  at  three  dairy  barns.  In  each  barn  the  milk  was  drawn  into 
small-topped  pails  and  strained  thru  a  combination  cloth  and  wire 
strainer  into  eight-gallon  cans.  After  each  milking,  the  utensils  were 
washed  in  water  containing  washing  powder,  rinsed  in  a  vat  of  tap 
water,  and  placed  on  a  rack.  At  each  milking  a  new  strainer  cloth 
was  used.  The  utensils  were  used,  as  a  rule,  in  from  six  to  twelve 
hours  after  being  washed,  altho  in  a  few  cases  cans  were  held  twenty- 
four  to  thirty-six  hours. 

Normally,  the  utensils  were  steamed  after  being  washed  at  these 
dairy  farms ;  but  in  order  to  bring  out  the  influence  of  unsteamed  uten- 
sils, the  steaming  was  omitted  on  some  days.  The  samples  of  milk 
were  removed  from  the  cans  for  bacteriological  examination  within 
one  hour  after  milking,  both  when  the  utensils  had  been  steamed  and 
when  they  had  been  left  unsteamed.  The  results  of  bacteriological 
examination  are  given  in  Tables  14  to  19. 

These  tables  present  a  striking  contrast  between  the  germ  content 
of  milk  handled  in  steamed  utensils  and  that  handled  in  unsteamed 
utensils.  When  the  pails,  the  strainers,  and  the  cans  were  steamed, 
only  4  cans  of  milk  out  of  34  in  Barn  I,  and  3  out  of  35  in  Barn  II 
had  a  germ  content  above  10,000  bacteria  per  cubic  centimeter.  The 
average  germ  content  for  all  the  milk  handled  in  steamed  utensils 
was  4,865  bacteria  per  cubic  centimeter  in  Barn  I  and  3,157  in  Barn 
II.  The  results  from  Barn  III  were  somewhat  higher,  the  average 
germ  content  being  12,400  per  cubic  centimeter  for  steamed  utensils. 

On  the  other  hand,  when  the  utensils  were  not  steamed,  the  germ 
content  of  the  milk  became  higher  and  more  variable.  Of  the  117  cans 


246 


BULLETIN   No.  204 


[February, 


of  milk  from  the  three  barns,  7  had  more  than  one  million  bacteria  per 
cubic  centimeter,  81  had  above  100,000,  and  only  2  had  less  than  10,000. 
The  highest  germ  content  in  a  single  can  was  2,623,100  and  the  lowest 
was  7,100.  The  average  germ  content  for  all  the  milk  handled  in 
unsteamed  utensils  was  311,000  for  Barn  I,  326,880  for  Barn  II,  and 
218,930  for  Barn  III. 

The  bacteria  that  were  found  in  the  milk  in  these  cans  were  con- 
tributed by  all  the  sources  of  contamination  to  which  the  milk  was 
exposed  on  its  way  from  the  udder  to  the  cans.  The  difference  between 
the  germ  content  of  the  milk  handled  in  the  steamed  utensils  and  that 

TABLE  14. — GERM  CONTENT  CF  MILK  HANDLED  IN.  STEAMED  PAILS,  STRAINERS, 

AND  CANS:     BARN  I 


No. 
of 
can 

Oct.  3,  1914, 
a.m. 

Oct.  4, 
a.m. 

May  12,  1915, 
a.m. 

May  13, 
a.m. 

May  21, 
a.m. 

May  22, 
a.m. 

May  25, 
a.m. 

Number  of  bacteria  per  cc.  of  milk  in  cans 

1 

2 
3 
4 
5 
6 
7 

1904 
2486 
3280 
2502 

1690 
1267 

6805 
5727 
5542 
7290 
10720 

3617 
3482 
3032 
1660 
3500 

15522 
6200 
4950 

8885 

12075 
1170 
5285 
3952 
4997 
4652 
2555 

826 
2600 
3592 
10510 
2712 
5837 
4600 

TABLE  15. — GERM  CONTENT  OF  MILK  HANDLED  IN  UNSTEAMED  PAILS,  STRAINERS, 

AND  CANS:    BARN   I 


No. 
of 
can 

May  3,  1915, 
p.m. 

May  4, 
a.m. 

May  5, 
p.m. 

May  6, 
a.m. 

May  6, 
p.m. 

May  7, 
a.m. 

Number  of  bacteria  per  cc.  of  milk  in  cans 

1 

2 
3 
4 
5 
6 

78700 

38400 
4560-0 
130  500 
7100 
28800 

624  500 

887  500 
763  100 
57100 
18200 
2  623  100 
9200 

108  000 
779  000 

120  000 
39100 
23200 
30200 
31200 
90400 

TABLE  16. — GERM  CONTENT  CF  MILK  HANDLED  IN  STEAMED  PAILS,  STRAINERS, 

AND  CANS:    BARN  II 


No. 

of 

Oct.  3,  1914, 
a.m. 

May  12,  1915, 
a.m. 

May  12, 
p.m. 

May  13, 
a.m. 

June  1, 
p.m. 

June  3, 
p.m. 

can 

Number  of  1 

Bacteria  per 

cc.  of  milk 

in  cans 

I 

o 

4 
5 
8 

7 

785 
610 
837 
235 
770 

5960 
1500 
2187 
19400  ' 
886 

850 
1985 
1616 
1722 
1977 
4027 
2  456 

1605 
1820 
2077 
1040 
6015 
2816 

6507 
1297 
11837 
4515 
4692 

1237 
942 
785 
1205 
1777 
10667 

8 

1837 

1918] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


247 


of  the  milk  handled  in  the  unsteamed  utensils  gives  approximately  the 
number  of  bacteria  contributed  by  the  unstcamed  pails,  strainers,  and 
cans.  From  the  foregoing  figures  this  difference  is  seen  to  be  306,135 
bacteria  per  cubic  centimeter  for  the  milk  handled  in  Barn  I ;  323,723 
bacteria  per  cubic  centimeter  for  the  milk  handled  in  Barn  II ;  and 
206,530  bacteria  per  cubic  centimeter  for  the  milk  handled  in  Barn 
III.  In  other  words,  the  unsteamed  pails,  strainers,  and  cans  added 
to  the  milk  64  times  as  many  bacteria  as  all  the  other  sources  of  con- 
tamination at  Barn  I,  103  times  as  many  in  Barn  II,  and  18  times  as 
many  in  Barn  III. 


TABLE  17. — GERM  CONTENT  OF  MILK  HANDLED  IN  UNSTEAMED  PAILS,  STRAINERS, 

AND  CANS:    BARN  II 


No. 

of 

April  27,  1915 
a.m. 

April  28, 
p.m. 

April  29, 
p.m. 

May  3, 
a.m. 

May  3, 
p.m. 

May  4, 

a.m. 

can. 

Number  o; 

bacteria  pe 

;r  cc.  of  mi] 

k  in  cans 

1 

2 
3 
4 
5 
6 
7 

212  000 
310  000 
97300 
123  500 
120  000 
124  700 
133  700 

89200 
363  500 
275  800 
111  200 
123  600 
422  500 
485  000 

18400 
52800 
21500 
32800 
35  100 
62  300 
73500 

828  000 
852  000 
410  500 
1  124  000 
369  000 
703  000 

118  700 
77100 
83900 
195  800 
61500 
111  100 
143  200 

426  200 
575  000 
254  700 
237  000 
554  000 
445  000 

May  4, 
p.m. 

May  5, 
a.m. 

May  5, 
p.m. 

May  6, 
a.m. 

May  6, 

p.m. 

May  7, 
a.m. 

j. 
2 
3 
4 
5 
6 

75000 
65300 
114  100 
158  300 
62500 
348  O'OO 

538  000 
172  200 
762  500 
630  500 
139  000 

208  500 
127  600 
399  700 
170  200 
223  700 
434  500 

1  135  000 
1  347  200 
544  600 
356  500 
1  053  700 
392  500 

127  400 
159  500 
298  400 
221  100 
107  500 
286  400 

690  000 
393  700 
127  700 
127  900 
1  520  000 
374  000 

7 

271500 

195  700 

279  000 

TABLE  18. — GERM  CONTENT  OF  MILK  HANDLED  IN  STEAMED  PAILS,  STRAINERS,  AND 

CANS:    BARN  III 


No. 
of 
can 

May  11,  1915 
p.m. 

May  12, 
a.m. 

May  12, 
p.m. 

May  13, 
a.m. 

June  1, 
p.m. 

June  3, 
p.m. 

Number  of  bacteria  per  cc.  of  milk  in  cans 

1 
2 

8295 
7980 

41150 
10737 

9652 
3782 

17  405 
4833 

5442 
13112 

6027 
20490 

TABLE  19. — GERM  CONTENT  OF  MILK  HANDLED  IN  UNSTEAMED  PAILS,  STRAINERS, 

AND  CANS:    BARN  III 


No. 
of 
can 

May  3,  1915 
a.m. 

May  3, 
p.m. 

May  4, 
a.m. 

May  4, 
p.m. 

May  5, 
a.m. 

May  5, 
p.m. 

May  6, 
a.m. 

May  6, 
p.m. 

May  7, 

a.m. 

Number  of  bacteria  per  cc.  of  milk  in  cans 

1 
2 

130  000 
25400 

40000 
37  200 

39800 
75400 

51700 
121  700 

154  700 
214  200 

109  000 
1  538  500 

335  500 
495  500 

183  400 
94100 

210  500 
84100 

248 


BULLETIN    No.   204 


[February, 


INFLUENCE  OF  UNSTEAMED  BOTTLE  FILLER  UPON  GERM  CONTENT 

OF  MILK 

The  bottle  filler  used  for  this  experiment  was  the  "double-end, 
four-quart  and  five-pint  filler"  shown  in  Fig.  1.  It  consisted  of  a  tank 
and  nine  valves,  each  valve  having  a  stem,  a  sleeve,  an  air  tube,  a  wire 
coil  spring,  and  a  rubber  washer. 

In  washing  the  bottle  filler  the  valves  were  taken  apart  and  placed 
inside  the  filler  tank.  The  tank  and  all  the  parts  were  then  scrubbed 
with  a  brush  and  washing  powder  and  rinsed  with  a  hose.  After 
the  bottler  was  cleaned  in,  this  manner,  it  remained  standing  in 
the  milk  room  about  twenty  hours  before  it  was  used  again.  When 
it  was  to  be  steamed,  it  was  covered  with  a  galvanized  iron  lid,  the 
valve  openings  were  stopped  with  corks,  and  the  steam  was  allowed 
to  flow  into  it  for  thirty  minutes.  The  steaming  was  done  about  one 
hour  before  bottling,  and  its  thoroness  was  always  tested  by  a  bac- 
teriological examination.  The  milk  bottles  were  steamed  in  all  cases. 

From  300  to  400  quarts  of  milk  were  pasteurized  and  bottled  each 
day.  The  milk  was  pasteurized  in  a  vat ;  then  cooled  in  the  same  vat 
by  passing  brine  thru  a  coil  revolving  in  the  milk;  and  then  it  was 
bottled  immediately.  Samples  of  the  milk  were  taken  from  the  pas- 
teurizing vat  just  before  bottling,  and  then  during  the  process,  from 
the  first  bottle  filled,  thru  one  of  the  four  valves  and  then  from  every 
ninth  bottle  filled  thru  the  same  valve.  Since  there  were  four  valves 
in  the  bottle  filler,  every  ninth  bottle  filled  thru  one  valve  was  actually 
every  thirty-sixth  bottle  filled. 

Table  20  gives  the  germ  content  of  the  milk  when  the  bottle  filler 
was  steamed,  and  Table  21  when  it  was  washed  but  not  steamed. 
The  bottles  in  both  cases  were  steamed  before  being  used. 

TABLE  20. — GERM  CONTENT  OF  PASTEURIZED  AND  BOTTLED  MILK  WHEN  BOTTLE 
FILLER  AND  BOTTLES  WERE  STEAMED:    DAIRY  A 


Samples  of 
milk  from: 

Jan.  4,  1916 

Jan.  5 

Jan.  6 

Jan.  7 

Jan.  8    |  Average 

Number  of  bacteria  per  cc.  of  milk 

Pasteurizer   

1832 
1887 
2782 
2165 
2257 
2250 
2  167 

265 
420 
260 
305 
255 
320 
230 

1497 
1270 
1310 
1637 

1287   . 
2027 
1  182 

100 
65 
40 
80 
50 
60 
395 

922 
1432 
1225 
916 
1090 
832 
1  180 

923 
1015 
1123 
1021 
969 
1098 
1  031 

1st   bottle  

36th           

72d             

108th          

144th          

180th 

Table  20  shows  that  when  the  bottle  filler  was  steamed  shortly 
before  use,  the  germ  content  of  the  bottled  milk  was  approximately 
the  same  as  that  in  the  pasteurizing  vat.  If  any  increase  took  place,  it 
was  not  measurable.  When,  however,  the  bottle  filler,  which  had 


GKRM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


249 


PH 


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250 


BULLETIN   No.  204 


[February, 


stood  for  twenty  hours  after  washing,  was  hot  steamed,  a  conspicuous 
increase  in  the  germ  content  of  the  bottled  milk  took  place.  Table  21 
for  instance,  shows  that  on  December  18  the  germ  content  of  the  milk 
in  the  pasteurizing  vat  was  but  60  bacteria  per  cubic  centimeter  while 
in  the  first  bottle  filled  it  was  increased  to  209,600  bacteria. 

The  averages  shown  in  the  last  column  in  Table  21  present  a 
striking  illustration  of  the  effect  of  the  unsteamed  bottle  filler  on  the 
germ  content  of  the  milk  passed  thru  it.  The  average  germ  content 


FIG.  1. — BOTTLE  FILLER  USED  IN  THE  EXPERIMENT 

of  the  milk  before  bottling  was  84  bacteria  per  cubic  centimeter ;  of  the 
first  bottle  filled  it  was  96,900 ;  and  of  the  last  bottle,  2,288.  There 
was  evidently  a  gradual  washing  out  of  the  bacteria  of  the  bottle  filler 
by  the  milk'  passed  thru  it,  the  greatest  proportion  being  removed  by 
the  first  milk.  However,  the  effect  of  the  unsteamed  bottler  was  evi- 
dent even  in  the  last  bottle  filled. 

COLLECTIVE  INFLUENCE)  OF  UTENSILS  AT  THE  BARN  AND  AT  THE  DAIRY 

In  the  barn  and  in  Dairy  A,  in  which  this  study  was  conducted, 
about  100  to  200  quarts  of  milk  came  into  contact  with  the  utensils 
during  the  process  of  milking.  The  utensils  used  comprized  five  pails, 
two  strainers,  two  weighing  pails,  one  sanitary  tube  fifteen  feet  long, 


1918} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


251 


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252  BULLETIN  No.   204  [February, 

one  clarifier,  one  tubular  cooler,  five  cans,  one  stirring  dipper,  and  one 
bottle  filler. 

The  utensils  were  steamed  on  certain  days,  while  on  other  days 
they  were  only  washed,  rinsed,  and  placed  on  a  rack  until  needed.  The 
bottles  were  steamed  in  all  cases. 

The  milk  was  bottled  within  two  hours  after  milking,  and  the 
samples  were  taken  from  the  consecutively  filled  bottles  at  definite 
intervals.  The  germ  content  of  the  milk  samples  from  steamed  uten- 
sils is  shown  in  Table  22,  and  from  unsteamed  utensils  in  Table  23. 

The  influence  of  the  unsteamed  utensils  is  measured  by  the  differ- 
ence in  the  germ  content  of  the  milk  handled  in  steamed  and  in  un- 
steamed utensils.  The  germ  content  of  the  milk  when  steamed  utensils 
were  used  represents  approximately  the  extent  of  contamination  from 
sources  other  than  from  the  utensils.  It  is  seen  from  Table  22  that  in 
most  cases  the  bottled  milk  handled  in  steamed  utensils  had  less  than 
5,000  bacteria  per  cubic  centimeter,  and  in  only  one  case  was  the  germ 
content  over  10,000.  On  the  other  hand,  when  unsteamed  utensils 
were  used,  as  shown  in  Table  23,  the  germ  content  of  the  bottled  milk 
became  variable  and  high.  The  lowest  count  was  51,000  bacteria  per 
cubic  centimeter  and  the  highest  1,085,000  bacteria. 

These  results  show  that  unsteamed  utensils  were  the  most  im- 
portant source  of  bacterial  contamination  at  this  dairy.  They  also 
show  that  when  the  utensils  were  thoroly  steamed,  milk  of  certified 
quality  was  produced  without  any  difficulty. 

INFLUENCE  OF  INDIVIDUAL  UTENSILS  AT  THE  BARN  AND  AT  THE  DAIRY 

This  experiment  on  the  influence  of  the  individual  utensils  was 
carried  on  at  the  same  barn  and  dairy  as  the  preceding  experiment. 
All  the  utensils  were  washed  and  rinsed  about  eight  hours  previous  to 
use.  and  only  the  bottles  were  steamed.  The  effect  of  the  utensils  that 
hold  milk,  such  as  cans  and  pails,  was  measured  from  samples  of  milk 
taken  directly  from  them.  The  effect  of  such  utensils  as  strainers 
and  clarifiers,  thru  which  milk  passes,  was  measured  from  samples 
taken  from  the  milk  after  it  had  run  into  steamed  cans. 

At  each  milking  two  lots  of  milk,  of  about  six  gallons  each,  were 
passed  one  after  the  other  thru  each  of  the  utensils  up  to  the  bottle 
filler,  and  samples  of  milk  were  removed  after  the  milk  came  into  con- 
tact with  each  utensil.  Both  lots  of  milk  were  then  mixed  in  the  bottle 
filler  and  bottled.  The  results  of  the  bacteriological  examination  of 
these  samples  are  presented  in  Table  24. 

In  the  preceding  experiments  it  was  shown  that  when  the  utensils 
were  steamed,  the  bottled  milk  at  this  dairy  rarely  exceeded  5,000 
bacteria  per  cubic  centimeter  (see  Table  22).  It  may  be  assumed, 
therefore,  with  reasonable  certainty  that  the  milk,  when  this  experi- 
ment was  performed,  did  not  receive  more  than  5,000  bacteria  per  cubic 


1918} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS 


253 


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254 


BULLKTIN    NO.    20-4 


[February, 


centimeter  from  the  sources  of  contamination  other  than  the  utensils. 
The  number  of  bacteria  each  utensil  added  to  the  milk  and  the  cumula- 
tive effect  of  a  number  of  utensils  upon  the  germ  content  of  the  milk 
is  very  evident  in  Table  24.  It  is  further  emphasized  in  Table  25, 
where  are  shown  the  average  numbers  of  bacteria  that  were  added  to 
the  milk  by  each  utensil  and  the  average  number  per  cubic  centimeter 
cf  the  milk. 

TABLE  25. — AVERAGE  NUMBER  OP  BACTERIA  ADDED  TO  FIFTY  LITERS  OF  MILK  BY 
THE  VARIOUS  UNSTEAMED  UTENSILS  IN  WHICH  IT  WAS  HANDLED:    DAIRY  A 


Source  of  bacteria 

Number  of  bacteria 
per  cc.  of  milk 

Total  number 
of  bacteria 

Sources  other  than  utensils  

5  000 

250  000  000 

3  pails  

54635 

2  731  750  000 

1  strainer  

7315 

365  750  000 

1  clarifier  tank   

8038 

401  900  000 

1  clarifier  ... 

141  340 

7  067  000  000 

1  cooler  

50900 

2  545  000  000 

1  bottle-filler  tank  

83246 

4  162  300  000 

Total  

350  000 

17  523  700  000 

Total  for  utensils.  . 

345  000 

17  273  700  000 

Each  utensil  is  seen  to  have  contributed  a  different  number  of 
bacteria  to  the  milk.  The  clarifier  and  the  bottle  filler  were  the  most 
prolific  sources.  The  clarifier  added,  on  the  average,  141,340  bacteria 
per  cubic  centimeter  of  the  50  liters  of  milk.  The  total  number  added 
by  the  bottle  filler  is  difficult  to  estimate,  since  the  valves  of  the  filler 
added  different  numbers  of  bacteria  to  the  consecutively  filled  bottles. 
A  rough  estimate  shows  that  the  tank  and  the  four  valves  of  ,the  filler 
added  approximately  436,000  bacteria  per  cubic  centimeter  of  the  milk. 

It  will  be  noticed  from  Table  24  that  the  first  lot  of  25  liters  of 
milk  passing  thru  the  utensils  became  more  heavily  seeded  with  bac- 
teria than  the  second  lot  of  25  liters.  As  the  milk  passed  thru  the 
valves  of  the  filler  into  the  bottles,  the  first  bottles  likewise  became 
more  heavily  contaminated  than  those  subsequently  filled.  There  is 
a  washing  out  of  the  bacteria  from  the  utensil  by  the  milk,  so  that 
the  influence  of  a  utensil  depends  on  the  amount  of  milk  passed  thru 
it  as  well  as  on  the  total  number  of  bacteria  in  the  utensil.  It  must 
therefore  be  borne  in  mind  that  in  this  experiment  only  50  liters  of 
milk  came  into  contact  with  the  utensils. 

Considered  as  a  whole,  the  accumulation  of  germ  life  in  milk'by 
contact  with  different  utensils  that  are  not  steamed,  frequently  reaches 
a  point  where  the  keeping  quality  of  the  milk  is  seriously  affected. 
The  milk  examined  in  this  last  experiment  was  less  than  two  hours  old. 
What  would  have  been  the  germ  content  of  this  milk  had  its  delivery 
to  the  consumer  been  delayed  some  twenty  to  forty  hours,  as  happens 
in  the  milk  business  in  large  cities,  is  readily  imagined. 


1G18]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  UTENSILS  256 

SUMMARY 

1.  BACTERIA  FOUND  IN  FRESHLY  WASHED  CANS. — An  examina- 
tion of  170  freshly  washed  but  unsteamed  milk  cans  showed  the  pres- 
ence of  large  numbers  of  bacteria.     Had  these  freshly  washed  cans 
been  filled  with  sterile  milk,  the  germ  content  of  the  milk  would  have 
varied  from  197  to  2,557,000  bacteria  per  cubic  centimeter  and  would 
have  averaged  128,592  bacteria  per  cubic  centimeter. 

2.  BACTERIA    FOUND   IN    CANS    THIRTY   HOURS    AFTER    BEING 
WASHED. — Fifty  cans  washed,  steamed,  and  left  thirty  hour's  uncov- 
ered and  inverted  on  a  rack,  if  filled  with  milk  would  have  added  to 
the  milk  an  average  of  8  bacteria  per  cubic  centimeter.     Fifty  c'ans 
similarly  cleansed  but  left  thirty  hours  with  the  lids  on,  if  filled  with 
milk  would  have  added  to  the  milk  an  average  of  1,816  bacteria  per 
cubic  centimeter. 

Fifty  cans  washed  but  not  steamed,  and  held  thirty  hours  uncov- 
ered and  inverted  on  a  rack,  if  filled  with  milk  would  have  added  to 
the  milk  an  average  of  27,164  bacteria  per  cubic  centimeter.  Ten  cans 
similarly  cleansed  but  held  thirty  hours  with  the  lids  on,  if  filled  with 
milk  would  have  added  to  the  milk  an  average  of  128,730  bacteria  per 
cubic  centimeter. 

3.  BACTERIA  FOUND  IN  CANS  WASHED  AND  RETURNED  TO  THE 
FARM. — Ninety-one  milk  cans  that  had  been  washed,   rinsed,   and 
steamed  at  the  dairy  and  covered  with  their  lids,  examined  as  they 
were  about  to  be  used  on  several  dairy  farms  showed  that  had  they 
been  filled  with  milk  they  would  have  added  to  the  milk  an  average  of 
23,523  bacteria  per  cubic  centimeter.     The  treatment  of  these  cans 
at  the  farms  was  not  uniform,  either  as  to  their  being  kept  covered  or 
as  to  the  length  of  time  elapsing  before  their  use. 

4.  SOURCES  OF  BACTERIA  IN  WASHED  CANS. — A  comparison  of  the 
germ  content  of  each  of  153  milk  cans  after  the  cans  had  been  emptied 
and  washed,  but  not  rinsed  or  steamed,  and  the  germ  content  of  the 
milk  previously  held  by  the  cans,  in  most  cases  revealed  no  direct  re- 
lationship.    However,  taken  in  the  whole,  the  dairy  which  received 
the  milk  with  the  higher  germ  content  also  had  the  cans  with  the 
higher  germ  content. 

An  examination  of  134  freshly  washed  cans  and  of  the  water  in 
which  they  were  washed  showed  that  the  wash  water  became  heavily 
seeded  with  bacteria  during  the  washing  process.  However,  the  ex- 
tremely large  numbers  of  bacteria  found  in  some  of  the  washed  cans 
could  not  be  accounted  for  by  contamination  from  the  wash  water. 
The  most  probable  explanation  of  these  extremely  large  numbers  is 
that  the  bacteria  are  imbedded  in  small  traces  of  grease  and  other 
matter  on  the  inner  walls  of  the  can,  and  become  loosened  in  the  wash- 
ing process. 


256  BULLETIN  No.  204  [February, 

5.  BACTERIA    FOUND    IN    BOTTLES    FRESHLY    WASHED    AND   IN 
BOTTLES  STANDING  TWENTY-FOUR  HOURS. — An  examination  of  154 
freshly  washed  but  unsteamed  milk  bottles  showed  that  had  they  been 
filled  with  sterile  milk,  the  germ  content  of  the  milk  would  have  aver- 
aged 1,339  bacteria  per  cubic  centimeter,  while  an  equal  number  of 
similar  bottles,  examined  after  an  interval  of  twenty-four  hours  dur- 
ing which  they  had  been  left  inverted  on  a  rack,  would  have  given 
a  germ  content  to  the  milk  of  12,930  bacteria  per  cubic  centimeter. 

6.  COLLECTIVE  INFLUENCE  OF  UTENSILS  AT  THE  BARN. — An  ex- 
amination of  81  cans  of  milk  at  the  farm  ready  for  transportation  to 
the  dairy,  when  all  utensils  had  been  carefully  steamed  showed  an 
average  germ  content  of  6,807  bacteria  per  cubic  centimeter.    A  simi- 
lar examination  of  the  milk  in  117  cans  from  the  same  farms,  when 
all  utensils  were  similarly  treated  except  that  the  steaming  was  omit- 
ted, showed  an  average  germ  content  of  285,600  bacteria  per  cubic 
centimeter. 

7.  INFLUENCE  OF  UNSTEAMED  BOTTLE  FILLER  UPON  GERM  CON- 
TENT OF  MILK. — When  the  bottle  filler  was  carefully  washed  and 
steamed,  it  exerted  no  appreciable  effect  upon  the  germ  content  of  the 
milk  passing  thru  it.    When  it  was  similarly  washed  but  not  steamed, 
the  germ  content  of  the  milk  of  the  first  bottle  was  increased  on  the 
average  by  96,900  bacteria  per  cubic  centimeter.    The  continued  use 
of  the  bottle  filler  gradually  washed  the  larger  part  of  the  germ  life 
from  the  machine. 

8.  COLLECTIVE  INFLUENCE  OF  UTENSILS  AT  THE  BARN  AND  AT  THE 
DAIRY. — A  study  of  the  collective  influence  of  all  the  utensils  that 
normally  come  into  contact  with  the  milk  both  at  the  barn  and  at  the 
dairy  showed  that  when  all  the  utensils  were  carefully  steamed  the 
germ  content  of  the  milk  in  the  bottles  was  about  4,566  bacteria  per 
cubic  centimeter.    When  similar  conditions  obtained  except  that  the 
steaming  of  the  utensils  was  omitted,  the  germ  content  of  the  milk 
approximated  257,240  bacteria  per  cubic  centimeter. 

9.  INFLUENCE  OF  INDIVIDUAL  UTENSILS  AT  THE  BARN  AND  AT  THE 
DAIRY. — Of  all  the  various  utensils  coming  into  contact  with  the  milk 
at  the  barn  and  at  the  dairy,  the  clarifier  and  the  bottle  filler  when 
unsteamed  proved  to  be  the  most  prolific  sources  of  contamination. 
The  clarifier  added  an  average  of  141,340  bacteria  per  cubic  centimeter 
to  the  fifty  liters  of  milk  passed  thru  it,  while  the  bottle-filler  tank  and 
the  four  valves  of  the  filler  added  approximately  436,000  bacteria  per 
cubic  centimeter  to  the  same  milk. 


1918]  GERM  CONTENT  OP  MILK  AS  INFLUENCED  BY  UTBNSILS  257 

CONCLUSIONS 

The  fact  that  the  dirt  which  falls  into  milk  at  the  barn  is  readily 
visible  in  the  milk  has  led  to  the  conclusion  that  the  barn  is  the 
principal  source  of  the  bacteria  in  milk.  The  results  of  this  study, 
however,  show  that  it  is  the  utensils,  rather  than  the  barn,  that  are 
largely  responsible  for  the  excessive  bacterial  contamination  of  milk. 
The  extent  of  the  contamination  of  milk  by  the  utensils  is  strikingly 
illustrated  in  one  of  the  experiments  in  this  study :  when  all  the  uten- 
sils commonly  used  for  handling  the  milk  at  the  barn  and  in  the  dairy 
were  thoroly  steamed,  the  bottled  milk  had  uniformly  only  about  5,000 
bacteria  per  cubic  centimeter,  but  as  soon  as  the  steaming  was  omitted 
the  bottled  milk  frequently  contained  several  hundred  thousand  bac- 
teria per  cubic  centimeter. 

The  cans  used  for  shipping  milk  are  a  particularly  prolific  source 
of  bacteria  when  they  are  washed  at  the  dairy  and  returned  to  the 
farm  without  being  thoroly  steamed  and  dried.  The  number  of  bac- 
teria usually  added  to  the  milk  by  such  cans  is  many  times  larger 
than  the  number  that  would  ordinarily  get  into  the  milk  at  the  barn ; 
the  addition  of  a  million  bacteria  per  cubic  centimeter  of  milk  by  such 
cans  is  not  uncommon. 

A  detailed  comparative  study  of  the  effect  of  the  various  other 
utensils  at  the  barn  and  at  the  dairy  suggests  that  the  greatest  contami- 
nation comes  from  the  more  complex  apparatus,  such  as. the  clarifier 
and  the  bottle  filler.  In  one  of  the  experiments  in  this  study,  it  was 
found  that  the  pails  added  approximately  eleven  times  as  many  bac- 
teria to  the  milk  as  the  barn  influences,  the  strainer  one  and  one-half 
times  as  many,  the  clarifier  thirty  times  as  many,  the  cooler  ten  times 
as  many,  and  the  bottle  filler  sixty  times  as  many — a  total  of  112  times 
as  many  added  by  the  utensils  as  by  the  barn  factors. 

It  seems  to  the  authors  that  in  an  attempt  to  produce  milk  with 
low  germ  content  too  much  stress  has  been  laid  on  practices  of  minor 
importance  and  the  influence  of  utensils  poorly  steamed  and  not  dried 
has  been  commonly  neglected. 


UNIVERSITY  OF  ILLINOIS-URBANA 


